I want to write a nested for loop that has to work in the bash shell prompt. nested for loop in Single line command.
For example,
for i in a b; do echo $i; done
a
b
In the above example, for loop is executed in a single line command right. Like this I have tried the nested for loop in the shell prompt. Its not working. How to do this. Please update me on this.
The question does not contain a nested loop, just a single loop. But THIS nested version works, too:
# for i in c d; do for j in a b; do echo $i $j; done; done
c a
c b
d a
d b
On one line (semi-colons necessary):
for i in 0 1 2 3 4 5 6 7 8 9; do for j in 0 1 2 3 4 5 6 7 8 9; do echo "$i$j"; done; done
Formatted for legibility (no semi-colons needed):
for i in 0 1 2 3 4 5 6 7 8 9
do
for j in 0 1 2 3 4 5 6 7 8 9
do
echo "$i$j"
done
done
There are different views on how the shell code should be laid out over multiple lines; that's about what I normally use, unless I put the next operation on the same line as the do (saving two lines here).
$(seq 0 9); in Bash, you could write for i in {0..9} too. There are lots of ways that could be used. The advantage of not using seq is that it saves on processes (11 of them). You're unlikely to find that's a problem, but it is a nominal reason for using one of the alternative notations (the one in the answer, or the brace expansion). Note that brace expansion is not very flexible - and neither is the written out list of numbers. The seq notation allows you to control the range with variable limits. It all depends on what you're after.#!/bin/bash
# loop*figures.bash
for i in 1 2 3 4 5 # First loop.
do
for j in $(seq 1 $i)
do
echo -n "*"
done
echo
done
echo
# outputs
# *
# **
# ***
# ****
# *****
for i in 5 4 3 2 1 # First loop.
do
for j in $(seq -$i -1)
do
echo -n "*"
done
echo
done
# outputs
# *****
# ****
# ***
# **
# *
for i in 1 2 3 4 5 # First loop.
do
for k in $(seq -5 -$i)
do
echo -n ' '
done
for j in $(seq 1 $i)
do
echo -n "* "
done
echo
done
echo
# outputs
# *
# * *
# * * *
# * * * *
# * * * * *
for i in 1 2 3 4 5 # First loop.
do
for j in $(seq -5 -$i)
do
echo -n "* "
done
echo
for k in $(seq 1 $i)
do
echo -n ' '
done
done
echo
# outputs
# * * * * *
# * * * *
# * * *
# * *
# *
exit 0
