How to use the read command in Bash

Question

When I try to use the read command in Bash like this   echo hello   read str echo  str   Nothing echoed  while I think str should contain the string hello  Can anybody please help me understand this behavior

User · Accepted Answer

The read in your script command is fine  However  you execute it in the pipeline  which means it is in a subshell  therefore  the variables it reads to are not visible in the parent shell  You can either   move the rest of the script in the subshell  too   echo hello     read str   echo  str    or use command substitution to get the value of the variable out of the subshell  str   echo hello  echo  str   or a slightly more complicated example  Grabbing the 2nd element of ls   str   ls     read a  read a  echo  a     echo  str

User · Answer

Typical usage might look like   i 0 echo -e  hello1 nhello2 nhello3    while read str   do     echo       i     str  done   and output  1  hello1 2  hello2 3  hello3

User · Answer

Other bash alternatives that do not involve a subshell   read str  lt  lt END               here-doc hello END  read str  lt  lt  lt   hello          here-string  read str  lt   lt  echo hello      process substitution

User · Answer

To put my two cents here  on KSH  reading as is to a variable will work  because according to the IBM AIX documentation  KSH s read does affects the current shell environment      The setting of shell variables by the read command affects the current shell execution environment    This just resulted in me spending a good few minutes figuring out why a one-liner ending with read that I ve used a zillion times before on AIX didn t work on Linux    it s because KSH does saves to the current environment and BASH doesn t

User · Answer

Do you need the pipe   echo -ne   MENU  read NUMBER

User · Answer

Another alternative altogether is to use the printf function   printf -v str  hello    Moreover  this construct  combined with the use of single quotes where appropriate  helps to avoid the multi-escape problems of subshells and other forms of interpolative quoting

User · Answer

I really only use read with  while  and a do loop     echo  This is NOT a test     while read -r a b c theRest  do   echo   a    b    theRest   done     This is a test  For what it s worth  I have seen the recommendation to always use -r with the read command in bash

User · Answer

The value disappears since the read command is run in a separate subshell  Bash FAQ 24

[bash] How to use the read command in Bash?

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