Shift Command in Shell Script in AIX and Linux

Shell in Unix never ceases to surprise. Stumbled upon 'shift 2' command in AIX few hours ago and it's very useful.

'Shift n' command shifts the parameters passed to a shell script by 'n' numbers to the left.

For example:

if you have a shell script which takes 3 parameters like:

./mytest.sh arg1 arg2 arg3

and you use shift 2 in your shell script, then the values of arg1 and arg2 will be lost and the value of arg3 will get assigned to arg1.

For example:

if you have a shell script which takes 2 parameters like:

./mytest arg1 and arg2

and you use shift 2, then values of both arg1 and arg2 will be lost.

Following is a working example of shift command in AIX:

testsrv>touch shifttest.sh

testsrv>chmod a+x shifttest.sh

testsrv>vi shifttest.sh

testsrv>cat shifttest.sh
#!/bin/ksh
SID=$1
BACKUP_TYPE=$2
echo "Before Shift: $1 and $2 => SID=$SID and BACKUPTYPE=$BACKUP_TYPE"
shift 2
echo "After Shift: $1 and $2 => SID=$SID and BACKUPTYPE=$BACKUP_TYPE"


testsrv>./shifttest.sh orc daily

Before Shift: orc and daily => SID=orc and BACKUPTYPE=daily
After Shift:  and  => SID=orc and BACKUPTYPE=daily


Note that the values of arguments passed has been shifted to left, but the values of variables has remained intact.