Trap, ERR, and echoing the error line

I'm trying to create some error reporting using a Trap to call a function on all errors:

Trap "_func" ERR

Is it possible to get what line the ERR signal was sent from? The shell is bash.

If I do that, I can read and report what command was used and log/perform some actions.

Or maybe I'm going at this all wrong?

I tested with the following:

#!/bin/bash

trap "ECHO $LINENO" ERR



echo hello | grep "asdf"

And $LINENO is returning 2. Not working.

edited May 29 '12 at 23:55

Gilles

540k12810941609

asked May 29 '12 at 18:23

Mechaflash

4923815

You can look at the bash debugger script bashdb. It seems that the first argument to trap can contain variables that are evaluated in the desired context. So trap 'echo $LINENO' ERR' should work.

– donothingsuccessfully
May 29 '12 at 18:53

hmm just tried this with a bad echo | grep command and it returns the line of the Trap statement. But I'll take a look at bashdb

– Mechaflash
May 29 '12 at 18:56

I'm so sorry... I didn't specify in my original question that I need a native solution. I edited the question.

– Mechaflash
May 29 '12 at 19:05

Sorry, I borked the example line: trap 'echo $LINENO' ERR. The first argument to trap is the entire echo $LINENO hardquoted. This is in bash.

– donothingsuccessfully
May 29 '12 at 19:43

4

@Mechaflash It would have to be trap 'echo $LINENO' ERR, with single quotes, not double quotes. With the command you wrote, $LINENO is expanded when line 2 is parsed, so the trap is echo 2 (or rather ECHO 2, which would output bash: ECHO: command not found).

– Gilles
May 29 '12 at 23:56

|
show 1 more comment

I'm trying to create some error reporting using a Trap to call a function on all errors:

Trap "_func" ERR

Is it possible to get what line the ERR signal was sent from? The shell is bash.

If I do that, I can read and report what command was used and log/perform some actions.

Or maybe I'm going at this all wrong?

I tested with the following:

#!/bin/bash

trap "ECHO $LINENO" ERR



echo hello | grep "asdf"

And $LINENO is returning 2. Not working.

edited May 29 '12 at 23:55

Gilles

540k12810941609

asked May 29 '12 at 18:23

Mechaflash

4923815

You can look at the bash debugger script bashdb. It seems that the first argument to trap can contain variables that are evaluated in the desired context. So trap 'echo $LINENO' ERR' should work.

– donothingsuccessfully
May 29 '12 at 18:53

hmm just tried this with a bad echo | grep command and it returns the line of the Trap statement. But I'll take a look at bashdb

– Mechaflash
May 29 '12 at 18:56

I'm so sorry... I didn't specify in my original question that I need a native solution. I edited the question.

– Mechaflash
May 29 '12 at 19:05

Sorry, I borked the example line: trap 'echo $LINENO' ERR. The first argument to trap is the entire echo $LINENO hardquoted. This is in bash.

– donothingsuccessfully
May 29 '12 at 19:43

4

@Mechaflash It would have to be trap 'echo $LINENO' ERR, with single quotes, not double quotes. With the command you wrote, $LINENO is expanded when line 2 is parsed, so the trap is echo 2 (or rather ECHO 2, which would output bash: ECHO: command not found).

– Gilles
May 29 '12 at 23:56

|
show 1 more comment

I'm trying to create some error reporting using a Trap to call a function on all errors:

Trap "_func" ERR

Is it possible to get what line the ERR signal was sent from? The shell is bash.

If I do that, I can read and report what command was used and log/perform some actions.

Or maybe I'm going at this all wrong?

I tested with the following:

#!/bin/bash

trap "ECHO $LINENO" ERR



echo hello | grep "asdf"

And $LINENO is returning 2. Not working.

edited May 29 '12 at 23:55

Gilles

540k12810941609

asked May 29 '12 at 18:23

Mechaflash

4923815

I'm trying to create some error reporting using a Trap to call a function on all errors:

Trap "_func" ERR

Is it possible to get what line the ERR signal was sent from? The shell is bash.

If I do that, I can read and report what command was used and log/perform some actions.

Or maybe I'm going at this all wrong?

I tested with the following:

#!/bin/bash

trap "ECHO $LINENO" ERR



echo hello | grep "asdf"

And $LINENO is returning 2. Not working.

bash shell-script error-handling trap

edited May 29 '12 at 23:55

Gilles

540k12810941609

asked May 29 '12 at 18:23

Mechaflash

4923815

edited May 29 '12 at 23:55

Gilles

540k12810941609

asked May 29 '12 at 18:23

Mechaflash

4923815

edited May 29 '12 at 23:55

Gilles

540k12810941609

edited May 29 '12 at 23:55

Gilles

540k12810941609

edited May 29 '12 at 23:55

Gilles

540k12810941609

asked May 29 '12 at 18:23

Mechaflash

4923815

asked May 29 '12 at 18:23

Mechaflash

4923815

asked May 29 '12 at 18:23

Mechaflash

4923815

You can look at the bash debugger script bashdb. It seems that the first argument to trap can contain variables that are evaluated in the desired context. So trap 'echo $LINENO' ERR' should work.

– donothingsuccessfully
May 29 '12 at 18:53

hmm just tried this with a bad echo | grep command and it returns the line of the Trap statement. But I'll take a look at bashdb

– Mechaflash
May 29 '12 at 18:56

I'm so sorry... I didn't specify in my original question that I need a native solution. I edited the question.

– Mechaflash
May 29 '12 at 19:05

Sorry, I borked the example line: trap 'echo $LINENO' ERR. The first argument to trap is the entire echo $LINENO hardquoted. This is in bash.

– donothingsuccessfully
May 29 '12 at 19:43

4

@Mechaflash It would have to be trap 'echo $LINENO' ERR, with single quotes, not double quotes. With the command you wrote, $LINENO is expanded when line 2 is parsed, so the trap is echo 2 (or rather ECHO 2, which would output bash: ECHO: command not found).

– Gilles
May 29 '12 at 23:56

|
show 1 more comment

You can look at the bash debugger script bashdb. It seems that the first argument to trap can contain variables that are evaluated in the desired context. So trap 'echo $LINENO' ERR' should work.

– donothingsuccessfully
May 29 '12 at 18:53

hmm just tried this with a bad echo | grep command and it returns the line of the Trap statement. But I'll take a look at bashdb

– Mechaflash
May 29 '12 at 18:56

I'm so sorry... I didn't specify in my original question that I need a native solution. I edited the question.

– Mechaflash
May 29 '12 at 19:05

Sorry, I borked the example line: trap 'echo $LINENO' ERR. The first argument to trap is the entire echo $LINENO hardquoted. This is in bash.

– donothingsuccessfully
May 29 '12 at 19:43

4

@Mechaflash It would have to be trap 'echo $LINENO' ERR, with single quotes, not double quotes. With the command you wrote, $LINENO is expanded when line 2 is parsed, so the trap is echo 2 (or rather ECHO 2, which would output bash: ECHO: command not found).

– Gilles
May 29 '12 at 23:56

You can look at the bash debugger script bashdb. It seems that the first argument to trap can contain variables that are evaluated in the desired context. So trap 'echo $LINENO' ERR' should work.

– donothingsuccessfully
May 29 '12 at 18:53

hmm just tried this with a bad echo | grep command and it returns the line of the Trap statement. But I'll take a look at bashdb

– Mechaflash
May 29 '12 at 18:56

I'm so sorry... I didn't specify in my original question that I need a native solution. I edited the question.

– Mechaflash
May 29 '12 at 19:05

Sorry, I borked the example line: trap 'echo $LINENO' ERR. The first argument to trap is the entire echo $LINENO hardquoted. This is in bash.

– donothingsuccessfully
May 29 '12 at 19:43

@Mechaflash It would have to be trap 'echo $LINENO' ERR, with single quotes, not double quotes. With the command you wrote, $LINENO is expanded when line 2 is parsed, so the trap is echo 2 (or rather ECHO 2, which would output bash: ECHO: command not found).

– Gilles
May 29 '12 at 23:56

|
show 1 more comment

3 Answers
3

active

oldest

votes

As pointed out in comments, your quoting is wrong. You need single quotes to prevent $LINENO from being expanded when the trap line is first parsed.

This works:

#! /bin/bash



err_report() {

    echo "Error on line $1"

}



trap 'err_report $LINENO' ERR



echo hello | grep foo  # This is line number 9

Running it:

 $ ./test.sh

 Error on line 9

edited Nov 6 '15 at 15:38

community wiki

3 revs, 3 users 92%
Mat

thanks for the example with a function call. I didn't know that double quotes expanded the variable in this case.

– Mechaflash
May 30 '12 at 14:23

echo hello | grep foo doesn't seem to throw error for me. Am I misunderstanding something?

– geotheory
Dec 2 '15 at 22:15

@geotheory On my system grep has an exit status of 0 if there was a match, 1 if there was no match and >1 for an error. You can check the behavior on your system with echo hello | grep foo; echo $?

– Patrick
Dec 7 '15 at 23:17

No you're right it is an error :)

– geotheory
Dec 8 '15 at 9:56

Don't you need to use -e on the invocation line, to cause error on command failure? That is: #!/bin/bash -e ?

– Tim Bird
Mar 31 '17 at 22:39

|
show 3 more comments

You can also use the bash builtin 'caller':

#!/bin/bash



err_report() {

  echo "errexit on line $(caller)" >&2

}



trap err_report ERR



echo hello | grep foo

it prints filename too:

$ ./test.sh

errexit on line 9 ./test.sh

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

add a comment |

I really like the answer given by @Mat above. Building on this, I wrote a little helper which gives a bit more context for the error:

We can inspect the script for the line which caused the failure:

err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR

Here it is in a small test script:

#!/bin/bash



set -e



err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR



echo one

echo two

echo three

echo four

false

echo five

echo six

echo seven

echo eight

When we run it we get:

$ /tmp/test.sh

one

two

three

four

Error occurred:

12      echo two

13      echo three

14      echo four

15   >>>false

16      echo five

17      echo six

18      echo seven

answered 46 mins ago

unpythonic

68236

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

As pointed out in comments, your quoting is wrong. You need single quotes to prevent $LINENO from being expanded when the trap line is first parsed.

This works:

#! /bin/bash



err_report() {

    echo "Error on line $1"

}



trap 'err_report $LINENO' ERR



echo hello | grep foo  # This is line number 9

Running it:

 $ ./test.sh

 Error on line 9

edited Nov 6 '15 at 15:38

community wiki

3 revs, 3 users 92%
Mat

thanks for the example with a function call. I didn't know that double quotes expanded the variable in this case.

– Mechaflash
May 30 '12 at 14:23

echo hello | grep foo doesn't seem to throw error for me. Am I misunderstanding something?

– geotheory
Dec 2 '15 at 22:15

@geotheory On my system grep has an exit status of 0 if there was a match, 1 if there was no match and >1 for an error. You can check the behavior on your system with echo hello | grep foo; echo $?

– Patrick
Dec 7 '15 at 23:17

No you're right it is an error :)

– geotheory
Dec 8 '15 at 9:56

Don't you need to use -e on the invocation line, to cause error on command failure? That is: #!/bin/bash -e ?

– Tim Bird
Mar 31 '17 at 22:39

|
show 3 more comments

As pointed out in comments, your quoting is wrong. You need single quotes to prevent $LINENO from being expanded when the trap line is first parsed.

This works:

#! /bin/bash



err_report() {

    echo "Error on line $1"

}



trap 'err_report $LINENO' ERR



echo hello | grep foo  # This is line number 9

Running it:

 $ ./test.sh

 Error on line 9

edited Nov 6 '15 at 15:38

community wiki

3 revs, 3 users 92%
Mat

thanks for the example with a function call. I didn't know that double quotes expanded the variable in this case.

– Mechaflash
May 30 '12 at 14:23

echo hello | grep foo doesn't seem to throw error for me. Am I misunderstanding something?

– geotheory
Dec 2 '15 at 22:15

@geotheory On my system grep has an exit status of 0 if there was a match, 1 if there was no match and >1 for an error. You can check the behavior on your system with echo hello | grep foo; echo $?

– Patrick
Dec 7 '15 at 23:17

No you're right it is an error :)

– geotheory
Dec 8 '15 at 9:56

Don't you need to use -e on the invocation line, to cause error on command failure? That is: #!/bin/bash -e ?

– Tim Bird
Mar 31 '17 at 22:39

|
show 3 more comments

As pointed out in comments, your quoting is wrong. You need single quotes to prevent $LINENO from being expanded when the trap line is first parsed.

This works:

#! /bin/bash



err_report() {

    echo "Error on line $1"

}



trap 'err_report $LINENO' ERR



echo hello | grep foo  # This is line number 9

Running it:

 $ ./test.sh

 Error on line 9

edited Nov 6 '15 at 15:38

community wiki

3 revs, 3 users 92%
Mat

As pointed out in comments, your quoting is wrong. You need single quotes to prevent $LINENO from being expanded when the trap line is first parsed.

This works:

#! /bin/bash



err_report() {

    echo "Error on line $1"

}



trap 'err_report $LINENO' ERR



echo hello | grep foo  # This is line number 9

Running it:

 $ ./test.sh

 Error on line 9

edited Nov 6 '15 at 15:38

community wiki

3 revs, 3 users 92%
Mat

edited Nov 6 '15 at 15:38

community wiki

3 revs, 3 users 92%
Mat

community wiki

3 revs, 3 users 92%
Mat

community wiki

3 revs, 3 users 92%
Mat

thanks for the example with a function call. I didn't know that double quotes expanded the variable in this case.

– Mechaflash
May 30 '12 at 14:23

echo hello | grep foo doesn't seem to throw error for me. Am I misunderstanding something?

– geotheory
Dec 2 '15 at 22:15

@geotheory On my system grep has an exit status of 0 if there was a match, 1 if there was no match and >1 for an error. You can check the behavior on your system with echo hello | grep foo; echo $?

– Patrick
Dec 7 '15 at 23:17

No you're right it is an error :)

– geotheory
Dec 8 '15 at 9:56

Don't you need to use -e on the invocation line, to cause error on command failure? That is: #!/bin/bash -e ?

– Tim Bird
Mar 31 '17 at 22:39

|
show 3 more comments

thanks for the example with a function call. I didn't know that double quotes expanded the variable in this case.

– Mechaflash
May 30 '12 at 14:23

echo hello | grep foo doesn't seem to throw error for me. Am I misunderstanding something?

– geotheory
Dec 2 '15 at 22:15

@geotheory On my system grep has an exit status of 0 if there was a match, 1 if there was no match and >1 for an error. You can check the behavior on your system with echo hello | grep foo; echo $?

– Patrick
Dec 7 '15 at 23:17

No you're right it is an error :)

– geotheory
Dec 8 '15 at 9:56

Don't you need to use -e on the invocation line, to cause error on command failure? That is: #!/bin/bash -e ?

– Tim Bird
Mar 31 '17 at 22:39

thanks for the example with a function call. I didn't know that double quotes expanded the variable in this case.

– Mechaflash
May 30 '12 at 14:23

echo hello | grep foo doesn't seem to throw error for me. Am I misunderstanding something?

– geotheory
Dec 2 '15 at 22:15

@geotheory On my system grep has an exit status of 0 if there was a match, 1 if there was no match and >1 for an error. You can check the behavior on your system with echo hello | grep foo; echo $?

– Patrick
Dec 7 '15 at 23:17

No you're right it is an error :)

– geotheory
Dec 8 '15 at 9:56

Don't you need to use -e on the invocation line, to cause error on command failure? That is: #!/bin/bash -e ?

– Tim Bird
Mar 31 '17 at 22:39

|
show 3 more comments

You can also use the bash builtin 'caller':

#!/bin/bash



err_report() {

  echo "errexit on line $(caller)" >&2

}



trap err_report ERR



echo hello | grep foo

it prints filename too:

$ ./test.sh

errexit on line 9 ./test.sh

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

add a comment |

You can also use the bash builtin 'caller':

#!/bin/bash



err_report() {

  echo "errexit on line $(caller)" >&2

}



trap err_report ERR



echo hello | grep foo

it prints filename too:

$ ./test.sh

errexit on line 9 ./test.sh

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

add a comment |

You can also use the bash builtin 'caller':

#!/bin/bash



err_report() {

  echo "errexit on line $(caller)" >&2

}



trap err_report ERR



echo hello | grep foo

it prints filename too:

$ ./test.sh

errexit on line 9 ./test.sh

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

You can also use the bash builtin 'caller':

#!/bin/bash



err_report() {

  echo "errexit on line $(caller)" >&2

}



trap err_report ERR



echo hello | grep foo

it prints filename too:

$ ./test.sh

errexit on line 9 ./test.sh

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

answered Jul 4 '17 at 9:34

Andrew Ivanov

11112

add a comment |

I really like the answer given by @Mat above. Building on this, I wrote a little helper which gives a bit more context for the error:

We can inspect the script for the line which caused the failure:

err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR

Here it is in a small test script:

#!/bin/bash



set -e



err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR



echo one

echo two

echo three

echo four

false

echo five

echo six

echo seven

echo eight

When we run it we get:

$ /tmp/test.sh

one

two

three

four

Error occurred:

12      echo two

13      echo three

14      echo four

15   >>>false

16      echo five

17      echo six

18      echo seven

answered 46 mins ago

unpythonic

68236

add a comment |

I really like the answer given by @Mat above. Building on this, I wrote a little helper which gives a bit more context for the error:

We can inspect the script for the line which caused the failure:

err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR

Here it is in a small test script:

#!/bin/bash



set -e



err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR



echo one

echo two

echo three

echo four

false

echo five

echo six

echo seven

echo eight

When we run it we get:

$ /tmp/test.sh

one

two

three

four

Error occurred:

12      echo two

13      echo three

14      echo four

15   >>>false

16      echo five

17      echo six

18      echo seven

answered 46 mins ago

unpythonic

68236

add a comment |

I really like the answer given by @Mat above. Building on this, I wrote a little helper which gives a bit more context for the error:

We can inspect the script for the line which caused the failure:

err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR

Here it is in a small test script:

#!/bin/bash



set -e



err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR



echo one

echo two

echo three

echo four

false

echo five

echo six

echo seven

echo eight

When we run it we get:

$ /tmp/test.sh

one

two

three

four

Error occurred:

12      echo two

13      echo three

14      echo four

15   >>>false

16      echo five

17      echo six

18      echo seven

answered 46 mins ago

unpythonic

68236

I really like the answer given by @Mat above. Building on this, I wrote a little helper which gives a bit more context for the error:

We can inspect the script for the line which caused the failure:

err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR

Here it is in a small test script:

#!/bin/bash



set -e



err() {

    echo "Error occurred:"

    awk 'NR>L-4 && NR<L+4 { printf "%-5d%3s%sn",NR,(NR==L?">>>":""),$0 }' L=$1 $0

}

trap 'err $LINENO' ERR



echo one

echo two

echo three

echo four

false

echo five

echo six

echo seven

echo eight

When we run it we get:

$ /tmp/test.sh

one

two

three

four

Error occurred:

12      echo two

13      echo three

14      echo four

15   >>>false

16      echo five

17      echo six

18      echo seven

answered 46 mins ago

unpythonic

68236

answered 46 mins ago

unpythonic

68236

answered 46 mins ago

unpythonic

68236

answered 46 mins ago

unpythonic

68236

add a comment |

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