How to Split a String into Two Substrings of Same Length Using Bash

bashstring

I would like to split a string into two halves and print them sequentially. For example:

abcdef

into

abc
def

Is there a simple way to do it, or it needs some string processing?

Best Answer

Using parameter expansion and shell arithmetic:

The first half of the variable will be:

${var:0:${#var}/2}

The second half of the variable will be:

${var:${#var}/2}

so you could use:

printf '%s\n' "${var:0:${#var}/2}" "${var:${#var}/2}"

You could also use the following awk command:

awk 'BEGIN{FS=""}{for(i=1;i<=NF/2;i++)printf $i}{printf "\n"}{for(i=NF/2+1;i<=NF;i++){printf $i}{printf "\n"}}'

$ echo abcdef | awk 'BEGIN{FS=""}{for(i=1;i<=NF/2;i++)printf $i}{printf "\n"}{for(i=NF/2+1;i<=NF;i++){printf $i}{printf "\n"}}'
abc
def

Related Solutions

Bash String Split – How to Split a String into an Array in Bash

Pure bash solution, no external tools used to process the strings, just parameter expansion:

#! /bin/bash
str='battery.charge: 90 battery.charge.low: 30 battery.runtime: 3690 battery.voltage: 230.0 device.mfr: MGE UPS SYSTEMS device.model: Pulsar Evolution 500'

IFS=: read -a fields <<< "$str"

for (( i=0 ; i < ${#fields[@]} ; i++ )) ; do
    f=${fields[i]}

    notfirst=$(( i>0 ))
    last=$(( i+1 == ${#fields[@]} ))

    (( notfirst )) && echo -n ${f% *}

    start=('' $'\n' ' ')
    colon=('' ': ')
    echo -n "${start[notfirst + last]}${f##* }${colon[!last]}"
done
echo

Explanation: $notfirst and $last are booleans. The part before the last space ${f% *} isn't printed for the first field, as there is no such thing. $start and $colon hold various strings that separate the fields: at the first item, notfirst + last is 0, so nothing is prepended, for the rest of the lines, $notfirst is 1, so a newline is printed, and for the last line, the addition gives 2, so a space is printed. Then, the part after the last space is printed ${f##* }. Colon is printed for all lines except the last one.

Bash – How to Split Single String into Character Array

s="hello"
declare -a a   # define array a
for ((i=0; i<${#s}; i++)); do a[$i]="${s:$i:1}"; done
declare -p a   # print array a in a reusable form

Output:

declare -a a='([0]="h" [1]="e" [2]="l" [3]="l" [4]="o")'

or (please note the comments)

s="hello"
while read -n 1 c; do a+=($c); done  <<< "$s"
declare -p a

Output:

declare -a a='([0]="h" [1]="e" [2]="l" [3]="l" [4]="o")'

Best Answer

Related Solutions

Bash String Split – How to Split a String into an Array in Bash

Bash – How to Split Single String into Character Array

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