Read from a standard input

Example on how to read from a standard input

• from a pipeline (the block {} is important)

echo "hello world" | { read foo; echo foo=$foo; }

• from a string

read foo <<< "Hello World"; echo foo=$foo;

• from a file. Example: All lines in an array (where \c0 replicate the eof character thanks to backslash escape)

IFS=$'\n' read -r -a REPO_DIRS -d $'\c0' < /path/to/myfile.csv

Get the first two words (fields) of a line

Read parse the line with the IFS separators and assign the value to the names defined, we can then use it to parse a line.

Example

echo "hello world, how do you do ?" | { read foo bar mi; echo foo=$foo bar=$bar mi=$mi; }

foo=hello bar=world, mi=how do you do ?

• tip: if you want to get rid of the command, add it as separator in IFS

echo "hello world, how do you do ?" | { IFS=" ," read foo bar mi; echo foo=$foo bar=$bar mi=$mi; }

foo=hello bar=world mi=how do you do ?

Loop line by line

This command:

• lists the file with the ls executable (ls -l)
• pipe the output to the condition of thewhile statement
• where the read condition splits the input by line and stores the line content in the lineVariable variable

ls -l | while read -r lineVariable; do
    echo Line: $lineVariable
done

Line: -rw-r--r-- 1 root root 1849173 May 13 2015 unixODBC-2.3.2.tar.gz
Line: -rwxr-xr-- 1 oracle oinstall 64 May 16 2017 whileDemo.sh

Name assignment

The first word is assigned to the first variable name, the second word to the second name, and so on, If there are :

• more words than names, leftover words, and their intervening separators are assigned to the last name.
• fewer words than names, the remaining names are assigned empty values.

The characters in IFS are used to split the line into words. The backslash character (\) may be used to remove any special meaning for the next character read and for line continuation.