setenv does not work from script

This post explains how to export a variable from a shell script to a tcsh parent shell.
 
consider the following script

hogwarts:~/x> cat setup_var.sh
#! /bin/tcsh -f

setenv a RAJU
echo $a

The executable bit is set on the script

hogwarts:~/x> chmod +x setup_var.sh
hogwarts:~/x> ls -al setup_var.sh
-rwxr-xr-x 1 rajulocal rajulocal 39 Jul  9 03:40 setup_var.sh 

I am using the tcsh shell

hogwarts:~/x> echo $0
tcsh

When executed, it shows that the variable "a" is getting the correct value

hogwarts:~/x> ./setup_var.sh
RAJU

However, the variable is not exported to the parent shell even though setenv is used in the script.

hogwarts:~/x> echo $a
a: Undefined variable.

The solution is to "source the script" instead of "dot executing".

hogwarts:~/x> source setup_var.sh
RAJU
hogwarts:~/x> echo $a
RAJU

Voila! Now the variable "a" is exported to the parent shell.

Happy shell script hacking...

Add a number to a variable in shell script

Consider the following shell script

$cat add_variables_02.sh
#! /bin/sh
ov=10;
nv=$((ov+3));      echo $nv
((nv=ov+3));       echo $nv
nv=$ov+3;          echo $nv
nv=`expr $ov+3`;   echo $nv
nv=`expr $ov + 3`; echo $nv

Execute in a shell

$bash add_variables_02.sh 
13
13
10+3
10+3
13

The first two methods nv=$((ov+3)) or ((nv=ov+3)) are faster than the fifth method nv=`expr $ov + 3` as the former uses bash's own feature and the later runs an external command in a subprocess.

Also, note that spaces are needed before and after the '+' character when expr is used.

Tested in Debian Wheezy machine using bash 4.2-1

Further reading

1. info coreutils 'expr invocation'
2. man expr
   

Special thanks to the anon 2011-08-24 5:06 AM for providing the first two methods.