Ok. I am starting to write linux Scipt files.

1. In my own script I didn't put #!/bin/bash or something similar to any line. Still my script worked. Why ?


2. Can I use pipes in scripts like

if [ `ls -al | grep filename` != "" ]; then
echo "file already exists."
exit 127;
fi


3. What scripting language is used with linux ( or with bash actually ). Is it just bash or is bash using perl or something ?

Thanks for your time.

1) The #! is call the she bang. It tells your shell what program to interpt the rest of the file with. If you don't specify a #! the default is /bin/sh

2) You can use pipes but in this case you should do this ...
another way would of been to check the $? after executing a command like this ...
no need for grep there.


3) what scripting language is used with linux? too many to list but here's a short list
tcl, bash, csh, sh, perl, python

Hi Markelo,
May be the oldest scripting language in *nix is the Bourne shell. Its executable file was "sh". It has some limitations but it was ubiquitous. When computers gained more power, the others started to appear like as "csh" which has a C like syntax, ksh (Korn shell) which maintains the Bourne shell syntax but has new commands and structures and, bash which is an acronym for "Bourne again shell". You can set up your profile to open your console always with one of these. The default for linux is bash. This setup is defined in "/etc/password", where the last field determines the user shell. Perl, python and tcl are powerful scripting languages, but normally not used at the console prompt.

Just to clarify (for clarity's sake), bash uses its own internal language for scripting. It does not (to my knowledge) require perl or any other scripting engine; it is a stand-alone interpreter.

OK. What I meaned was that does it works like a perl interpreter and thus would follow perl grammer or is it different language by itself.

For another matter I would still like to know how I can pipe something to grep witin my scripts. That ls -al | grep filename was just an example.

Ok in truth I was trying to do
lsmod | grep fglrx

You can give help in that also, but please help me with pipe.

When if-grepping, there's often no need for the '[' and ']'.

Just do:
"Grep" is the last command in the pipe-line, and as such it provides an exit code for the "if" to use as a condition. When grep finds the string it exits with zero code . If it does not find it, with non-zero exit code. That's all "if" needs.

That's what I was trying to say: bash uses an internal, stand-alone interpreter. In that respect, it follows its own grammar, syntax, etc.

Yes, you can use pipes as much as you like within backticks ( ` ). You can pipe one command into another, or have a string of 5 pipes, 10 pipes, or more.

You can use backticks in if statements like your original post, or you can assign it to a variable:
The two code snippets above are equivalent. Hko's code is also equivalent. He's directly using the return result of grep, whereas the code above is explicitly testing for grep's failing output (an empty string).