How to convert a string from uppercase to lowercase in Bash

Question

I have been searching to find a way to convert a string value from upper case to lower case  All the search results show approaches of using tr command   The problem with the tr command is that I am able to get the result only when I use the command with echo statement  For example   y  HELLO  echo  y  tr    upper       lower      The above works and results in  hello   but I need to assign the result to a variable as below   y  HELLO  val  y  tr    upper       lower    string  val world   When assigning the value like above it gives me an empty result   PS  My Bash version is 3 1 17

User · Answer

The correct way to implement your code is

y="HELLO"
val=$(echo "$y" | tr '[:upper:]' '[:lower:]')
string="$val world"

This uses $(...) notation to capture the output of the command in a variable. Note also the quotation marks around the string variable -- you need them there to indicate that $val and world are a single thing to be assigned to string.

If you have bash 4.0 or higher, a more efficient & elegant way to do it is to use bash builtin string manipulation:

y="HELLO"
string="${y,,} world"

User · Answer

Note that tr can only handle plain ASCII  making any tr-based solution fail when facing international characters   Same goes for the bash 4 based   x    solution   The awk tool  on the other hand  properly supports even UTF-8   multibyte input   y  HELLO  val   echo   y    awk   print tolower  0     string   val world    Answer courtesy of liborw

User · Answer

This worked for me  Thank you Rody   y  HELLO  val   echo  y   tr    upper       lower     string   val world    one small modification  if you are using underscore next to the variable You need to encapsulate the variable name in      string    val  world

User · Answer

Why not execute in backticks     x  echo   y    tr    upper       lower        This assigns the result of the command in backticks to the variable x   i e  it s not particular to tr but is a common pattern solution for shell scripting   You can use       instead of the backticks  See here for more info

User · Answer

If you define your variable using declare  old  typeset  then you can state the case of the value throughout the variable s use     declare -u FOO AbCxxx   echo  FOO ABCXXX    -l  does lc

User · Answer

I m on Ubuntu 14 04  with Bash version 4 3 11  However  I still don t have the fun built in string manipulation   y     This is what I used in my script to force capitalization   CAPITALIZED  echo    y     tr   a-z     A-Z

User · Answer

If you are using bash 4 you can use the following approach   x  HELLO  echo  x    HELLO  y   x    echo  y    hello  z   y    echo  z    HELLO   Use only one   or   to make the first letter lowercase or uppercase

[string] How to convert a string from uppercase to lowercase in Bash?

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