Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
present).
bash$ diff −r ~/notes1 ~/notes2
Only in /home/bozo/notes1: file02
Only in /home/bozo/notes1: file03
Only in /home/bozo/notes2: file04
diff3
Use zdiff to compare gzipped files.
An extended version of diff that compares three files at a time. This command returns an exit value of
0 upon successful execution, but unfortunately this gives no information about the results of the
comparison.
bash$ diff3 file−1 file−2 file−3
====
1:1c
This is line 1 of "file−1".
2:1c
This is line 1 of "file−2".
3:1c
This is line 1 of "file−3"
sdiff
cmp
Compare and/or edit two files in order to merge them into an output file. Because of its interactive
nature, this command would find little use in a script.
The cmp command is a simpler version of diff, above. Whereas diff reports the differences between
two files, cmp merely shows at what point they differ.
Like diff, cmp returns an exit status of 0 if the compared files are identical, and 1 if
they differ. This permits use in a test construct within a shell script.
Example 12−27. Using cmp to compare two files within a script.
#!/bin/bash
ARGS=2 # Two args to script expected.
E_BADARGS=65
E_UNREADABLE=66
if [ $# −ne "$ARGS" ]
then
echo "Usage: `basename $0` file1 file2"
exit $E_BADARGS
fi
if [[ ! −r "$1" || ! −r "$2" ]]
then
echo "Both files to be compared must exist and be readable."
exit $E_UNREADABLE
fi
cmp $1 $2 &> /dev/null # /dev/null buries the output of the "cmp" command.
Chapter 12. External Filters, Programs and Commands 185