What linux shell command returns a part of a string? [duplicate]

Question

This question already has an answer here:

• Extract substring in Bash 20 answers

I want to find a linux command that can return a part of the string. In most programming languages, it's the substr() function. Does bash have any command that can be used for this purpose. I want to be able to do something like this... substr "abcdefg" 2 3 - prints cde.

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Subsequent similar question:

• Extract substring in Bash

Answer 1

If you are looking for a shell utility to do something like that, you can use the cut command.

To take your example, try:

echo "abcdefg" | cut -c3-5

which yields

cde

Where -cN-M tells the cut command to return columns N to M, inclusive.

Answer 2

From the bash manpage:

${parameter:offset}
${parameter:offset:length}
        Substring  Expansion.   Expands  to  up  to length characters of
        parameter starting at the character  specified  by  offset.
[...]

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Or, if you are not sure of having bash, consider using cut.

Answer 3

In "pure" bash you have many tools for (sub)string manipulation, mainly, but not exclusively in parameter expansion :

${parameter//substring/replacement}
${parameter##remove_matching_prefix}
${parameter%%remove_matching_suffix}

Indexed substring expansion (special behaviours with negative offsets, and, in newer Bashes, negative lengths):

${parameter:offset}
${parameter:offset:length}
${parameter:offset:length}

And of course, the much useful expansions that operate on whether the parameter is null:

${parameter:+use this if param is NOT null}
${parameter:-use this if param is null}
${parameter:=use this and assign to param if param is null}
${parameter:?show this error if param is null}

They have more tweakable behaviours than those listed, and as I said, there are other ways to manipulate strings (a common one being $(command substitution) combined with sed or any other external filter). But, they are so easily found by typing man bash that I don't feel it merits to further extend this post.

Answer 4

In bash you can try this:

stringZ=abcABC123ABCabc
#       0123456789.....
#       0-based indexing.

echo ${stringZ:0:2} # prints ab

More samples in The Linux Documentation Project

Answer 5

expr(1) has a substr subcommand:

expr substr <string> <start-index> <length>

This may be useful if you don't have bash (perhaps embedded Linux) and you don't want the extra "echo" process you need to use cut(1).

Answer 6

${string:position:length}