Bash-Beginners-Guide

Bash Guide for Beginners
cathy ~> grep -c false /etc/passwd
7
cathy ~> grep -i ps ~/.bash* | grep -v history
/home/cathy/.bashrc:PS1="\[\033[1;44m\]$USER is in \w\[\033[0m\] "
With the first command, user cathy displays the lines from /etc/passwd containing the string root.
Then she displays the line numbers containing this search string.
With the third command she checks which users are not using bash, but accounts with the nologin shell are
not displayed.
Then she counts the number of accounts that have /bin/false as the shell.
The last command displays the lines from all the files in her home directory starting with ~/.bash,
excluding matches containing the string history, so as to exclude matches from ~/.bash_history which
might contain the same string, in upper or lower cases. Note that the search is for the string "ps", and not for
the command ps.
Now let's see what else we can do with grep, using regular expressions.
4.2.2. Grep and regular expressions
If you are not on Linux
We use GNU grep in these examples, which supports extended regular expressions. GNU grep is the
default on Linux systems. If you are working on proprietary systems, check with the -V option which
version you are using. GNU grep can be downloaded from http://gnu.org/directory/.
4.2.2.1. Line and word anchors
From the previous example, we now exclusively want to display lines starting with the string "root":
cathy ~> grep ^root /etc/passwd
root:x:0:0:root:/root:/bin/bash
If we want to see which accounts have no shell assigned whatsoever, we search for lines ending in ":":
cathy ~> grep :$ /etc/passwd
news:x:9:13:news:/var/spool/news:
To check that PATH is exported in ~/.bashrc, first select "export" lines and then search for lines starting
with the string "PATH", so as not to display MANPATH and other possible paths:
cathy ~> grep export ~/.bashrc | grep '\