I'm writing a bash script that compares two directories, but I'm not sure how to check conditions
For example, if the user enters 1 arg instead of 2 (we need 2 since we're comparing two directories), it should give an error. If both arg are valid, compare the directories and output to a file.
Processing arguments that are passed via a script's command line is as simple as follows. Say we had this script:
$ cat cmd.bash
#!/bin/bash
echo "arg1: $1"
echo "arg2: $2"
Now run with no arguments:
$ ./cmd.bash
arg1:
arg2:
With 1 argument:
$ ./cmd.bash hi
arg1: hi
arg2:
With 2 arguments:
$ ./cmd.bash hi bye
arg1: hi
arg2: bye
You can then check if the arguments, 1 & 2, are valid directories or not, and then bail out or proceed as needed. So we introduce 2 checks to see if the 2 arguments are directories or not, if not then exit.
$ cat cmd.bash
#!/bin/bash
[ -d "$1" ] || exit
[ -d "$2" ] || exit
[ $# == 2 ] || exit
echo "arg1: $1"
echo "arg2: $2"
Say we have these directories.
$ mkdir d1 d2
$ ls -l
total 12
-rwxrwxr-x. 1 saml saml 89 Oct 14 23:13 cmd.bash
drwxrwxr-x. 2 saml saml 4096 Oct 14 23:14 d1
drwxrwxr-x. 2 saml saml 4096 Oct 14 23:14 d2
If we are given anything other than 2 directories, the script will simply exit.
$ ./cmd.bash hi bye
If we're given 2 directories:
$ ./cmd.bash d1 d2
arg1: d1
arg2: d2
If we're given more than 2 arguments:
$ ./cmd.bash d1 d2 d3
I'll leave the comparison of the 2 directories to you. For learning Bash I'd direct you to the link below for a free online book on Bash.
The number of arguments is in the parameter $#.
if [ $# -ne 2 ]; then
echo 1>&2 "Usage: $0 DIRECTORY1 DIRECTORY2"
exit 3
fi
If you want to enforce that the arguments are both directories (as opposed to other types of files), test them with -d.
The utility diff compares two files. With the option -r, it compares directories recursively.
diff -ru -- "$1" "$2"
