Bash – Split single string into character array using ONLY bash

bashsplitstring

I want to split 'hello' into h e l l o in an array using only bash, I could do it in sed with sed 's/./& /g' but I want to know how to split a string into an array in Bash when I do not know what the delimiter would be, or the delimiter is any single character. I don't think I can use ${i// /} without some creativity because the delimiter is an unknown, and I don't think that expression accepts regex. I tried using BASH_REMATCH with [[ string =~ ([a-z].).* ]] but it doesn't work as I expected. What is the proper way to use only bash to accomplish a string.split() type of behavior? The reason is that I am trying to write the rev utility in all bash:

  while read data; do
  word=($(echo $data|tr ' ' '_'|sed 's/./& /g'))
  new=()
  i=$((${#word[@]} - 1))
  while [[ $i -ge 0 ]]; do
    new+=(${word[$i]})
    (( i-- ))
  done
  echo ${new[@]}|tr -d ' '|tr '_' ' '
  done

But I used tr and sed, I want to know how to do the split properly and then I will fix it to be all bash. Just for fun.

Best Answer

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")'

Related Solutions

Bash – Use awk to split line into array and use that array’s values in calling shell

I think that you can do what you want without awk:

cat "${smryfile}" | while IFS=: read first last varx
do
    echo "first='$first' last='$last' varx='$varx'"
    # do something
done

This produces:

first='Joe' last='Johnson' varx='25'
first='Sue' last='Miller' varx='27'

Note that this approach will work even if some names in the file include spaces.

Note also that the use of cat above is not necessary:

while IFS=: read first last varx
do
    echo "first='$first' last='$last' varx='$varx'"
    # do something
done <"${smryfile}"

A side benefit of removing cat, as per the above, is that any variables that you create in the loop will survive after the loop finishes.

Bash – 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.

Best Answer

Related Solutions

Bash – Use awk to split line into array and use that array’s values in calling shell

Bash – How to split a string into an array in bash

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