Adding spaces to stdout - bash

Question

Is it possible to add spaces to the left of every output to stdout (and stderr if possible) when I run commands in a bash shell script?
I'd like to do something like:
#!/bin/bash
echo Installing: Something
echo " => installing prerequisite1"
## INSERT MAGICAL LEFT SPACES COMMAND HERE ##
apt-get install -q -y prerequisite
## ANOTHER MAGICAL CANCELLING LEFT SPACES COMMAND HERE ##
echo " => installing prerequisite2"
# ... the padding again ...
wget http://abc.com/lostzilla.tar.gz
tar vzxf lostzilla.tar.gz
cd lostzilla-1.01
./configure
make && make install
# ... end of padding ...
echo Done.
Any idea?
EDIT: Added quotes to the echo command, otherwise they won't be padded.

Answer 1

Yes, you can quote them for simple things:
echo ' => installing prerequisite1'
and pipe the output through sed for complex things:
tar vzxf lostzilla.tar.gz 2>&1 | sed 's/^/ /'
The 2>&1 puts stdout and stderr onto the stdout stream and the sed replaces every start-of-line marker with three spaces.
How well this will work on something like wget which does all sorts of cursor manipulations I'm not sure.
Example shown here:
pax> ls -1 p*
phase1.py
phase1.sh
phase2.py
phase2.sh
primes.c
primes.exe
primes.sh
primes.stat
pax> ls -1 p* | sed 's/^/ /'
phase1.py
phase1.sh
phase2.py
phase2.sh
primes.c
primes.exe
primes.sh
primes.stat
One trick I've used in the past is to ensure that the scripts themselves take care of the indentation:
#!/bin/bash
if [[ "${DONT_EVER_SET_THIS_VAR}" = "" ]] ; then
export DONT_EVER_SET_THIS_VAR=except_for_here
$0 | sed 's/^/ /'
exit
fi
ls -1 p*
This will re-run the script with indentation through sed if it's not already doing so. That way, you don't have to worry about changing all your output statements. A bit of a hack, I know, but I tend to just do what's necessary for quick-and-dirty shell scripts.

Answer 2

If you want to turn spacing on and off, use the following awk script:
#!/usr/bin/gawk -f
/^#SPACEON/ { spaces=1; }
/^#SPACEOFF/ { spaces=0; }
!/^#SPACE/ {
if(spaces) {
print " " $0;
} else {
print $0;
}
}
Note that there are slight problems with your bash scipt. Notably, the use of => in your echo statements will output the character = to the file "installing".
#!/bin/bash
echo Installing: Something
echo '=> installing prerequisite1'
echo '#SPACEON'
echo You would see apt-get install -q -y prerequisite
echo '#SPACEOFF'
echo '=> installing prerequisite2'
echo '#SPACEON'
echo You would see wget http://abc.com/lostzilla.tar.gz
echo You would see tar vzxf lostzilla.tar.gz
echo You would see cd lostzilla-1.01
echo You would see ./configure
echo You would see make \&\& make install
echo '#SPACEOFF'
echo Done.
Combining the two gives me:
$ ./do-stuff | ./magic-spacing
Installing: Something
=> installing prerequisite1
You would see apt-get install -q -y prerequisite
=> installing prerequisite2
You would see wget http://abc.com/lostzilla.tar.gz
You would see tar vzxf lostzilla.tar.gz
You would see cd lostzilla-1.01
You would see ./configure
You would see make && make install
Done.
Where do-stuff is your bash script and magic-spacing is my awk script above.

Answer 3

Depending on how the command writes to stdout, you can just indent with a simple awk script:
$ echo -e 'hello\nworld' | awk '{print " ",$0}'
hello
world

Answer 4

Quite un-magical you can use printf to do the following:
# space padding for single string
printf "%-4s%s\n" "" "=> installing prerequisite1"
# space padding for single command output
# use of subshell leaves original IFS intact
( IFS=$'\n'; printf " %s\n" $(command ls -ld * 2>&1) )
# note: output to stderr is unbuffered
( IFS=$'\n'; printf " %s\n" $(command ls -ld * 1>&2) )
It's also possible to group commands by enclosing them in curly braces and space-padd their output like so:
{
cmd1 1>&2
cmd2 1>&2
cmd3 1>&2
} 2>&1 | sed 's/.*/ &/'

Answer 5

It's possible to redirect stdout to stderr script/shell-wide using exec ...
(
exec 1>&2
command ls -ld *
) 2>&1 | sed 's/^/ /'

Answer 6

Use python pyp (The Pyed Piper):
ls -ld | pyp "' '+p"