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About bash : How-to-split-one-string-into-multiple-strings-separated-by-at-least-one-space-in-bash-shell

Question Detail

I have a string containing many words with at least one space between each two. How can I split the string into individual words so I can loop through them?

The string is passed as an argument. E.g. ${2} == “cat cat file”. How can I loop through it?

Also, how can I check if a string contains spaces?

Question Answer

I like the conversion to an array, to be able to access individual elements:

sentence=”this is a story”
stringarray=($sentence)

now you can access individual elements directly (it starts with 0):

echo ${stringarray[0]}

or convert back to string in order to loop:

for i in “${stringarray[@]}”
do
:
# do whatever on $i
done

Of course looping through the string directly was answered before, but that answer had the the disadvantage to not keep track of the individual elements for later use:

for i in $sentence
do
:
# do whatever on $i
done

See also Bash Array Reference.
……………………………………………………
Did you try just passing the string variable to a for loop? Bash, for one, will split on whitespace automatically.

sentence=”This is a sentence.”
for word in $sentence
do
echo $word
done

 

This
is
a
sentence.

……………………………………………………
Probably the easiest and most secure way in BASH 3 and above is:
var=”string to split”
read -ra arr <<<"$var" (where arr is the array which takes the split parts of the string) or, if there might be newlines in the input and you want more than just the first line: var="string to split" read -ra arr -d '' <<<"$var" (please note the space in -d ''; it cannot be omitted), but this might give you an unexpected newline from <<<"$var" (as this implicitly adds an LF at the end). Example: touch NOPE var="* a *" read -ra arr <<<"$var" for a in "${arr[@]}"; do echo "[$a]"; done Outputs the expected [*] [a] [*] as this solution (in contrast to all previous solutions here) is not prone to unexpected and often uncontrollable shell globbing. Also this gives you the full power of IFS as you probably want: Example: IFS=: read -ra arr < <(grep "^$USER:" /etc/passwd) for a in "${arr[@]}"; do echo "[$a]"; done Outputs something like: [tino] [x] [1000] [1000] [Valentin Hilbig] [/home/tino] [/bin/bash] As you can see, spaces can be preserved this way, too: IFS=: read -ra arr <<<' split : this ' for a in "${arr[@]}"; do echo "[$a]"; done outputs [ split ] [ this ] Please note that the handling of IFS in BASH is a subject on its own, so do your tests; some interesting topics on this: unset IFS: Ignores runs of SPC, TAB, NL and on line starts and ends IFS='': No field separation, just reads everything IFS=' ': Runs of SPC (and SPC only) Some last examples: var=$'\n\nthis is\n\n\na test\n\n' IFS=$'\n' read -ra arr -d '' <<<"$var" i=0; for a in "${arr[@]}"; do let i++; echo "$i [$a]"; done outputs 1 [this is] 2 [a test] while unset IFS var=$'\n\nthis is\n\n\na test\n\n' read -ra arr -d '' <<<"$var" i=0; for a in "${arr[@]}"; do let i++; echo "$i [$a]"; done outputs 1 [this] 2 [is] 3 [a] 4 [test] BTW: If you are not used to $'ANSI-ESCAPED-STRING' get used to it; it's a timesaver. If you do not include -r (like in read -a arr <<<"$var") then read does backslash escapes. This is left as exercise for the reader. For the second question: To test for something in a string I usually stick to case, as this can check for multiple cases at once (note: case only executes the first match, if you need fallthrough use multiple case statements), and this need is quite often the case (pun intended): case "$var" in '') empty_var;; # variable is empty *' '*) have_space "$var";; # have SPC *[[:space:]]*) have_whitespace "$var";; # have whitespaces like TAB *[^-+.,A-Za-z0-9]*) have_nonalnum "$var";; # non-alphanum-chars found *[-+.,]*) have_punctuation "$var";; # some punctuation chars found *) default_case "$var";; # if all above does not match esac So you can set the return value to check for SPC like this: case "$var" in (*' '*) true;; (*) false;; esac Why case? Because it usually is a bit more readable than regex sequences, and thanks to Shell metacharacters it handles 99% of all needs very well. ............................................................ Just use the shells "set" built-in. For example, set $text After that, individual words in $text will be in $1, $2, $3, etc. For robustness, one usually does set -- junk $text shift to handle the case where $text is empty or start with a dash. For example: text="This is a test" set -- junk $text shift for word; do echo "[$word]" done This prints [This] [is] [a] [test] ............................................................ $ echo "This is a sentence." | tr -s " " "\012" This is a sentence. For checking for spaces, use grep: $ echo "This is a sentence." | grep " " > /dev/null
$ echo $?
0
$ echo “Thisisasentence.” | grep ” ” > /dev/null
$ echo $?
1

……………………………………………………
(A) To split a sentence into its words (space separated) you can simply use the default IFS by using

array=( $string )

Example running the following snippet

#!/bin/bash

sentence=”this is the \”sentence\” ‘you’ want to split”
words=( $sentence )

len=”${#words[@]}”
echo “words counted: $len”

printf “%s\n” “${words[@]}” ## print array

will output

words counted: 8
this
is
the
“sentence”
‘you’
want
to
split

As you can see you can use single or double quotes too without any problem

Notes:
— this is basically the same of mob’s answer, but in this way you store the array for any further needing. If you only need a single loop, you can use his answer, which is one line shorter 🙂
— please refer to this question for alternate methods to split a string based on delimiter.

(B) To check for a character in a string you can also use a regular expression match.
Example to check for the presence of a space character you can use:

regex=’\s{1,}’
if [[ “$sentence” =~ $regex ]]
then
echo “Space here!”;
fi

……………………………………………………
echo $WORDS | xargs -n1 echo

This outputs every word, you can process that list as you see fit afterwards.
……………………………………………………
For checking spaces just with bash:

[[ “$str” = “${str% *}” ]] && echo “no spaces” || echo “has spaces”

……………………………………………………
$ echo foo bar baz | sed ‘s/ /\n/g’
foo
bar
baz

……………………………………………………
For my use case, the best option was:
grep -oP ‘\w+’ file

Basically this is a regular expression that matches contiguous non-whitespace characters. This means that any type and any amount of whitespace won’t match. The -o parameter outputs each word matches on a different line.
……………………………………………………
Another take on this (using Perl):
$ echo foo bar baz | perl -nE ‘say for split /\s/’
foo
bar
baz

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