How to check the output of diff command in shell script?

Question

I have to compare a file with 3 different golden files using diff. I need to exit the script with exit 0 if test file is the same as any of the three golden files.

I tried the following:

#!/bin/sh
one=`diff -q NEW_GOLDEN_OUTPUT_ASYNC_1 /tmp/tmp_last_lines.log`
two=`diff -q NEW_GOLDEN_OUTPUT_ASYNC_2 /tmp/tmp_last_lines.log`
three=`diff -q NEW_GOLDEN_OUTPUT_ASYNC_3 /tmp/tmp_last_lines.log`

if [[ $one || $two || $three ]]; then
  exit 0
else
  exit 1
fi

But it returns exit 0 in all cases. I'm using /bin/ksh shell. Any suggestions?

To check if two files are identical use if cmp -s "$source_file" "$dest_file"; then : # files are the same else : # files are different fi — chipmunk
– chipmunk, Commented Dec 7, 2012 at 10:13

Aaron Digulla · Accepted Answer · 2012-12-07 10:23:47Z

1

Your code looks at the output of diff but you should look at the exit code. Try this instead:

#!/bin/sh
diff -q NEW_GOLDEN_OUTPUT_ASYNC_1 /tmp/tmp_last_lines.log && \
diff -q NEW_GOLDEN_OUTPUT_ASYNC_2 /tmp/tmp_last_lines.log && \
diff -q NEW_GOLDEN_OUTPUT_ASYNC_3 /tmp/tmp_last_lines.log

&& will only execute the next command if the previous one succeeded.

Alternatively, use set -e (Exit immediately if a command exits with a non-zero status.):

#!/bin/sh
set -e
diff -q NEW_GOLDEN_OUTPUT_ASYNC_1 /tmp/tmp_last_lines.log
diff -q NEW_GOLDEN_OUTPUT_ASYNC_2 /tmp/tmp_last_lines.log
diff -q NEW_GOLDEN_OUTPUT_ASYNC_3 /tmp/tmp_last_lines.log

answered Dec 7, 2012 at 10:23

Aaron Digulla

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