eolas/Programming_Languages/Shell/Read.md

categories	tags
Programming Languages	shell

read

The primary use of read is to capture user input from stdin. It is also often used frequently to parse strings or files that are redirected to it (with < and <<) or piped to it. In each case, what is read is stored as a variable.

read will parse line by line using a space (\n) as the default delimiter. You can use IFS to parse by other characters and/or split the contents into an array.

Example of capturing user input

$ read var1 var2
$ thomas bishop # user inputs this
$ echo $var2
$ bishop

If you don't specify variables, read will automatically parse using whitespace

Example of piping to read

This reads the files in a directory and passes the file names to read.

find -type -f  -not -path "./.git/" | read $fname

Example of parsing a file

We will typically read from a source and then do something with each variable that read returns, e.g:

while read var; do
  if [var == 'something']; then
    # do something
done < './input-file.txt

$REPLY

If you do not assign a variable name to store the value that read reads a default ($REPLY) is applied. You can reference this value in your code.

For example the following loop does something if $REPLY is equal to an empty string:

while read;
do
    ((count++))
    if [[ -z "$REPLY" ]]; then
        echo "$count"
    fi
done < "$input