In Bash you can use for loop to iterate over a number of things. This tutorial shows how to use two Bash for loops in a simple way!

Bash has two for loops:

1. C-style loop that iterates through an index variable:

   # semicolon is required when "do" is on the same line
   for (( expr1; cond; expr2 )); do
      commands...
   done
   

   Example:

   $> for ((i=0; i < 3; ++i)); do echo $i; done
   0
   1
   2
   

2. Another kind of for loop is for-each kind:

   for VAR in SEQUENCE; do
      commands...
   done
   

   sequence can be any list of things, like files, output of commands, etc. Examples will clarify

   Use for loop to iterate over list of files:

   $> for f in /bin/c*; do ls $f; done
   /bin/cat
   /bin/chacl
   /bin/chgrp
   /bin/chmod
   /bin/chown
   /bin/chvt
   /bin/cp
   /bin/cpio
   

   for loop to iterate over list of numbers:

   $> for i in 1 2 3; do echo $i; done
   1
   2
   3
   

   for loop to iterate over generated range of numbers:

   # from 0 to 6, with step 2
   $> for i in {0..6..2}; do echo $i; done
   0
   2
   4
   6
   

   for loop to iterate over result lines of subcommand:

   $> for i in $(ls /bin/d*); do echo $i; done
   /bin/dash
   /bin/date
   /bin/dd
   /bin/df
   /bin/dir
   /bin/dmesg
   /bin/dnsdomainname
   /bin/domainname
   /bin/dumpkeys
   

   When [in LIST] is not specified, then $@ (input parameters) is used.

   Bash for loops are really powerful and flexible. Use them in your shell scripts and command line!