Egrep ERE to find null

Shell Programming and Scripting
1

Hello All,
My apologies if a similar question has already been posted. I searched for "grep", "egrep" and "null"

I'm having an issue with egrep and an extended regular expression.
I'm doing a test for a job name. I would like to have the user enter a job name with no spaces and also test to make sure that they don't accidently hit the return key too fast.
My code:

echo "Please enter a job name (no spaces): "
read jobname
#  ***test not working*** while [`echo $jobname | egrep '(" "|"^$")' | wc -l -gt 0 ]; do
 
while [`echo $jobname | grep " " | wc -l -gt 0 ] || [`echo $jobname | grep "^$" | wc -l -gt 0 ]; do   # working
echo "Please enter a new job name (NO spaces): "
read jobname
done

The command egrep '(" "|"^$")' isn't working!!! It doesn't give any errors but it never goes through the while statement from any test.
Thanks in advanced!!

2

It is safer to have while not followed by the "okay" expression.
The following ensures there is only and at least one non-blank characters:

while ! echo "x$jobname" | egrep '^x[^[:blank:]]+$' >/dev/null
do
 echo "Please enter a new job name (NO spaces): "
 read jobname
done

The quotes are necessary for safety. Also further references should quote "$jobname".
The x is for additional safety, e.g. to escape a user input "-n" that has a special meaning in echo.
More strict is to test for at least one alphanumeric character:

while ! echo "x$jobname" | egrep '^x[[:alnum:]]+$' >/dev/null
3 
#! /bin/bash

echo "Enter job name:"
read x

while [ 1 ]
do
    echo $x | egrep -q "^$|^ *$"
    if [ $? -eq 0 ]
    then
        echo "No blank lines or spaces. Enter job name:"
        read x
    else
        break
    fi
done

echo $x
4

There's not just one but many easy ways to test with pure shell builtins:

if [ -z "$VARTOTEST" ] || [ "$VARTOTEST" = " " ]
then
        echo "$VARTOTEST empty or one space"
fi

case "$VARTOTEST" in
) echo "blank" ;;
 ) echo "one space" ;;
*) echo "not blank" ;;
esac

VAR=""
case X in $VARTOTEST ; do VAR="$X" ; done
if [ -z "$VAR" ]
then
        echo "$VARTOTEST is blank, or one or more spaces"
fi

set -- $VARTOTEST

if [ -z "$1" ]
then
        echo "$VARTOTEST blank, or one or more spaces"
fi

And these are just the pure bourne ways. If I knew you had bash or ksh I could suggest simpler ways using their string operations.

5 
while [`echo $jobname | grep " " | wc -l -gt 0 ] || [`echo $jobname | grep "^$" | wc -l -gt 0 ]; do  # working

Are you sure that is "working"? The backticks starts before echo, but they don't stop. Compare:

while [`echo $jobname | grep " " | wc -l` -gt 0 ] || [`echo $jobname | grep "^$" | wc -l` -gt 0 ]; do  # working
6

Thanks!!

This is what I ended up using that works

while [`echo $jobname | egrep '^[^[:blank:]]+$' | wc -l -gt 0 ]; do

MadeInGermany: I'm unaware of what the "x" in your example does. I'm not asking for a long winded explanation, although you may. If you don't mind give me a viable resource where I may read up on that functionality!

balaisuri: thanks for helping. I did try the ERE of "^$|^ *$" and it didn't work at least not on my system. it catches null but doesn't catch a line with a space.

Corona688: Thanks for the many responses. I'll have to wait till I have more time to go through your methods.

7

That's way too convoluted. It may "work", but it's too confusing to put into long-term source code. And it is grammatically incorrect, as I pointed out before. I would look at the other suggestions that were made, as you indicated you want to do.

8

The main thing is the "quotes".
Please run the script, enter a * and see what happens...

echo -n x

suppresses line feed
Therefore the escape with

echo x-n x

But actually not needed when quoted

echo "-n x"

You don't need back-ticks and count the output characters if you take the exit status from egrep, as in my example.

---------- Post updated at 04:14 PM ---------- Previous update was at 04:05 PM ----------

while ! can be written as until

until echo "$jobname" | egrep '^[^[:blank:]]+$' >/dev/null
do
...