PatchLog

If you want to compare two strings in shell you can use something like

test "$str1" = "$str2" but that will only tell you if the strings are equal. The strcmp(3) C function also tells you if the first string is less or greater then the second ( alphabetically) . I created a similar function in shell.

My function takes two arguments and compares them alphabetically. My idea was to put the strings in a list, sort the list and then verify which string is the first in the list.

This function returns 0 if the strings are equal, -1 (actually 255 because you can't return a negative value from a function) if the first string is less then the second and 1 if the second argument is greater then the first.

function strcmp
{
local s1="$1"
local s2="$2"
if [ "$s1" = "$s2" ] ; then
        return 0
fi
r=$(echo -e -n "$s1n$s2"|sort|head -n 1)
if [ "$r" = "$s1" ] ; then
        return -1
fi
if [ "$r" = "$s2" ] ; then
        return 1
fi
}

Update:
The built in test for bash 3.x supports string ">" and "<" for strings :

STRING1 < STRING2
True if STRING1 sorts before STRING2 lexicographically.
STRING1 > STRING2
True if STRING1 sorts after STRING2 lexicographically.

so we can rewrite the function like this :

 
function strcmp
{
if [ "$1" = "$2" ] ; then
return 0
fi
if [ "$1" '>' "$2" ] ; then
return 1
fi
return -1
}

So if you have bash 3.x use the new function because it's faster

Update 2:
you can also do it using expr like this :

 
function strcmp
{
if [ "$1" = "$2" ] ; then
return 0
fi
if expr "$1" ">" "$2" ; then
return 1
fi
return -1
}
 

This entry was posted on Friday, April 20th, 2007 at 6:51 pm and is filed under shell. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.