Access $? Variable with a piped statement? - bash

Question

I have some code that I would like to have the $? variable of.
VARIABLE=`grep "searched_string" test.log | sed 's/searched/found/'`
Is there any way to test if this entire line (rather than just the sed command) was completed successfully? If I try the following code right after it:
if [ "$?" -ne 0 ]
then
echo 1
exit
fi
it doesn't run even if the grep part of the statement fails.
Could someone show how to resolve this issue?

Answer 1

Use the
echo ${PIPESTATUS[#]}
will print out the array of exit-statuses of all commands.
$ ls | grep . | wc -l
28
$ echo ${PIPESTATUS[#]}
0 0 0
but
$ ls | grep nonexistentfilename | wc -l
0
$ echo ${PIPESTATUS[#]}
0 1 0 #the grep returns 1 - pattern not found
or
$ ls nonexistentfilename | grep somegibberish | wc -l
ls: nonexistentfilename: No such file or directory
0
$ echo ${PIPESTATUS[#]}
1 1 0 #ls and grep fails
for exact command status
echo ${PIPESTATUS[1]} #for the grep
also here is the
set -o pipefail
from the docs
pipefail
If set, the return value of a pipeline is the value of the
last (rightmost) command to exit with a non-zero status, or zero if
all commands in the pipeline exit successfully. This option is
disabled by default.
$ ls nonexistentfile | wc -c
ls: nonexistentfile: No such file or directory
0
$ echo $?
0
$ set -o pipefail
$ ls nonexistentfile | wc -c
ls: nonexistentfile: No such file or directory
0
$ echo $?
1
EDIT based on the comment
Youre probably tried the next:
VARIABLE=$(grep "searched_string" test.log | sed 's/searched/found/')
echo "${PIPESTATUS[#]}"
Of course, this can't work because the whole $(...) part runs in the subshell (another process) and therefore any variable what is created is lost when the subshell exits. (at the ))
You should put the whole PIPESTATUS mechanism into $(...) like next:
variable=$(
grep "searched_string" test.log | sed 's/searched/found/'
# do something with PIPESTATUS
# you should not echo anythig to stdout (because will be captured into $variable)
# you can echo on stderr - e.g.
echo "=${PIPESTATUS[#]}=" >&2
)
Also, the second line of the comment is an solution, eg:
var_with_status=$(command | commmand2 ; echo ":DELIMITER:${PIPESTATUS[#]}")
now, the $var_with_status will contain not only the result of the command | command2 but the PIPESTATUS too, delimited with some unique delimiter, so you can extract it...
Also, the set -o pipefail will indicate the result - if you don't need exact place of the fail.
Also you can write the PIPESTATUS in some temp-file (in the subshell) and the parent can read it and delete the temp-file...
Also is possible print the PIPESTATUS into different file-descriptors in the subshell and read this descriptor in the parent shell, but....
... beware do not fall into the XY problem, where you will make extremelly complicated script, only because you don't want change the logic of the processing.
e.g. you can always break you script into safe parts, like:
var1=$(grep 'str' test.log)
#check the `$var1` and do something with the error indicated with `$?`
var2=(sed '....' <<<"$var1")
#check the `$var2` and do something with the error indicated with `$?`
#and so on
simple enough?
So, ask yourself - do you really need mungling with how to get the PIPESTATUS form an subshell?
Ps: don't use uppercase variable names. could interfere with some environment variables and causes hard-to-debug problems..