Bash for

External

• http://ss64.com/bash/for.html

Internal

• bash

Overview

The for built-in command expand words, and execute commands once for each member in the resultant list, with i bound to the current member.

   for i in words; do commands; done

Alternatively, for:

   for i do commands; done

commands executes for each positional parameter (as if in "$@" had been specified.

Yes another alternative form:

    for (( i=0; i<${#names[@]}; i++ )); do
        local name=${names[${i}]}
        echo "${name}"
    done

Iterating through $1, $2, $3 ...

The Simple Version

     for i do
         echo ${i}
     done

Using the Argument Array

TODO

Iterating through a space separated list

    s="a b c"
    for i in ${s}
        do
            echo ${i}
        done

or

     s="a b c"
     for i in ${s}; do echo ${i}; done

Note the use of ";"

Iterating over Lines in the Same bash Process

IFS="$(printf '\n\r')"
for line in $(cat ./file.txt); do
   echo "${line}"
done
IFS="$(printf ' \t\n')"

Note 1 Be careful when setting IFS before a for loop, even if you restore the default value after the loop: everything inside the loop will use the non-standard IFS value and it may not work as expected.

For more details on IFS and possible pitfalls while using it, see IFS.

Note 2 This method does not work very well when the file is large, the content of the file will be first buffered in memory so the loop will appear irresponsive, at least for a while.

Iterating over a File List

Use a globbing expression after in and the shell will replace it with the list of files matching the expression:

for f in dir/B*; do
    echo ${f}
done

If file names match, the replacement closely matches the expression (example "dir/BMW.txt dir/Bentley.txt").

In case no filename match, the for body is executed with he literal expression ("dir/B*" in the example above).