Using sed

2014-03-17T09:31:29-04:00

sed stands for stream editor.

This is the most common way of my sed usage:

echo [SOMETHING] | sed 's/old/NEW/g'

Based on that, I have this tcsh alias¹ to get timestamps that I use to append to quick tar backups.

alias gettimestamp 'date | tr " :" "__" | sed '"'"'s/_[0-9]*_EDT.*//g'"'"''

Learn about sed from [here][s1].

Note how single quotes are escaped inside single-quoted alias definitions in tcsh. [s1]: http://www.grymoire.com/Unix/Sed.html ↩︎

Writing aliases with optional arguments in tcsh

2014-03-12T11:46:49-04:00

Some times I would need to define an alias in tcsh which can have optional arguments. tcsh doesn’t seem to support that directly.

Here’s how I solve that problem.

If you have an alias alias test 'echo \!:1*' and if you run test abc def, you will get the output abc def.

!:1* prints out all the arguments starting from argument 1 till the last where even argument 1 is optional. If that argument doesn’t exist, the variable will be assigned a null value.

But tcsh will not complain about it – the * after !:1 is the beauty. On the other hand, if I have an alias alias test2 'echo \!:1', and if I run test – with zero arguments – tcsh will give an error.

So extending that, I have the below alias defined to grab an argument of any index.

alias opt_args 'set arg1 = `echo \!:1* | awk '"'"'{ print $1 }'"'"'`; \\
                echo -n "Arg num 1 = $arg1 "; \\
                set arg2 = `echo \!:2* | awk '"'"'{ print $1 }'"'"'`; \\
                echo -n "Arg num 2 = $arg2 "; \\
                set arg3 = `echo \!:3* | awk '"'"'{ print $1 }'"'"'`; \\
                echo -n "Arg num 3 = $arg3 "; \\
                echo ""; \\
               '

You can test this alias by running these commands:

opt_args abc
opt_args abc def
opt_args abc def ghi
opt_args abc def ghi jkl

alias on A Scripter's Notes

Using sed

Writing aliases with optional arguments in tcsh