echo command breaks lines, being used in loops [duplicate]
In my file 'foo' there is a first line: 'a b', and the second line: 'c d':
$ cat foo
a b
c d
I want to print in terminal in loop these two lines: one after another:
$ for i in $(cat foo); do echo $i; done
But in the output 'echo' command breaks the order, so instead of having:
a b
c d
I actually have:
a
b
c
d
Solution 1:
for i in $(cat foo) does not loop lines but words (or fields) split by your field separator $IFS. It default to \n\t (space, newline, tab).
If you change your field separator to newline only, you can use your command as is (Disclaimer: please read below!):
IFS=$'\n'
for i in $(cat foo); do echo $i; done
You might want to make a backup of IFS to restore it later:
OLD_IFS="$IFS"
.
.
.
IFS="$OLD_IFS"
Output:
a b
c d
However, this is considered bad practice.
- Bit Better:
while IFS= read -r line; do ... done < file - Much better: Use a dedicated tool for your task such as
grep,sedorawk.
Please read Why is using a shell loop to process text considered bad practice?.
Solution 2:
You can use while read for this purpose
[/tmp]$ while read line ; do echo $line ; done < foo
a b
c d
Adding a separator for your understanding
[/tmp]$ while read line ; do echo $line ; echo "----" ; done < foo
a b
----
c d
----
[/tmp]$