Quoting

Newsgroups:  comp.unix.shell
Date:        Mon, 30 Oct 2006 07:47:22 -0500

> I was reviewing the Suse/Gentoo run-crons script, and comparing it with
> some elementary scripts I had written. All of a sudden, I realized that
> despite reading the docs and advanced scripting manual, I really did not
> have a good grasp on the concept of when to quote, enclose in a brace, etc.
>
> This snippet crystallizes my confusion. ... For that matter, when would
> the assignment to LOCKDIR have to be quoted? If there is a whitespace?
>
> LOCKDIR=/var/spool/cron/lastrun
> LOCKFILE=${LOCKDIR}/lock
>
> echo "braces no quotes $LOCKFILE"
>
> LOCKFILE="${LOCKDIR}"/lock
> echo "braces quote $LOCKFILE"
>
> LOCKFILE=$LOCKDIR/lock
> echo "no braces no quote $LOCKFILE"
>
> LOCKFILE="$LOCKDIR"/lock
> echo "no braces quote $LOCKFILE"

LOCKFILE=${LOCKDIR}1/lock

LOCKFILE="$LOCKDIR/lock file with spaces"

STRINGWITHSPACES="foo     bar"
echo $STRINGWITHSPACES
echo "$STRINGWITHSPACES"

OTHERSTRING=$STRINGWITHSPACES

eval cd \"`cat ~/.pfm/cwd | strh hm_ca`\"

++ cat /home/tong/.pfm/cwd
++ strh hm_ca
+ eval cd '"~/s/tdRaw/pan"'
++ cd '~/s/tdRaw/pan'
bash: cd: ~/s/tdRaw/pan: No such file or directory

eval cd `cat ~/.pfm/cwd | strh hm_ca`

++ cat /home/tong/.pfm/cwd
++ strh hm_ca
+ eval cd '~/s/tdRaw/pan'
++ cd /home/tong/s/tdRaw/pan

$ sh -xc 'filesb=`ls -A`; echo $filesb | od -c'
++ ls -A
+ filesb=etc
usr
+ echo etc usr
+ od -c
0000000   e   t   c       u   s   r  \n
0000010

$ sh -xc 'filesb=`ls -A`; echo "$filesb" | od -c'
++ ls -A
+ filesb=etc
usr
+ echo 'etc
usr'
+ od -c
0000000   e   t   c  \n   u   s   r  \n
0000010

Newsgroups:  comp.unix.shell
Date:        Sun, 16 Oct 2005 17:44:52 +0200

> How to quote within the "$()" in posix compatible shells?
>
> I tried all the following but none of them worked. I need the "$()"
> notation because it is actually part of my long expression that have more
> "$()" in it.
>
> fname='a b c'
> echo "$(basename $fname)"
> echo "$(basename '$fname')"
> echo "$(basename \"$fname\")"
> echo "$(basename ${fname})"

echo "$(basename "$fname")"

fname='a  b c'
$ echo "$(basename "$fname")"
a  b c

> changing your `sh' to `sh -x' will let you
> see exactly what is happening:

> cmd=echo $x | sed "s/xxx/yyy/"
> + echo $x | sed "s/xxx/yyy/"
> + eval x=$x | sed "s/xxx/yyy/"
> + sed s/xxx/yyy/
> x=---xxx---
> + echo ---xxx---
> ---xxx---
>
> the command substitution on the line with the eval, you will note,
> gets expanded before the eval happens, meaning all the eval sees as
> a command line to evaluate is "x=$x".  so what happens is that you
> assign x to itself, and then pipe the output of that (which is nothing)
> to the sed command.

sh -vx << 'eof'
echo "###"
x="---xxx---"
cmd='eval echo $x | sed "s/xxx/yyy/"'
x=`$cmd`
echo $x
echo "###"
eof

>>
cmd='eval echo $x | sed "s/xxx/yyy/"'
cmd=eval echo $x | sed "s/xxx/yyy/"
x=`$cmd`
+ eval echo $x | sed "s/xxx/yyy/"
+ + sedecho ---xxx---
 s/xxx/yyy/
x=---yyy---
echo $x
+ echo ---yyy---
>>

>I just can't make the following alias works:
>
>mytestalias='awk -F'"' ...'

alias myt="awk -F'\"' ..."

>I've tried
>
>mytestalias=awk -F'"' ...

alias mytestalias=awk\ -F'\"'\ ...

>mytestalias='awk -F\'\"\' ...'

alias mytestalias='awk -F\" ...'

bash$ alias sqt='sed "s/'\''/'\''\\\\'\'''\''/g; s/^/'\''/; s/$/'\''/"'

bash$ alias sdq='echo '

bash$ sqt
sed "s/'/'\\\\''/g; s/^/'/; s/$/'/"
'sed "s/'\''/'\''\\\\'\'''\''/g; s/^/'\''/; s/$/'\''/"'

bash$ sdq 'sed "s/'\''/'\''\\\\'\'''\''/g; s/^/'\''/; s/$/'\''/"'
sed "s/'/'\\\\''/g; s/^/'/; s/$/'/"

bash$

> I know I can use
>
> xterm -e sh -c 'command;echo Type Control-d to close window;cat'
>
> to invoke a predefined command, Now, how to make it into a sh
> function so that I can use any arbitrary commands?
>
> I've tried to come up with the following, but none of them works:
>
> testit(){ xterm -e sh -c "'$@;echo Type Control-d to close window;cat'" & }

testit(){ xterm -e sh -c "$*;echo Type Control-d to close window;cat" & }

Date: 1999-08-24

> > >  case "$VAR" in
> > Heck, with case you don't even need the quotes:
> >    case $VAR in
> >      YES) ... ;;
> >    esac
>
>  Hrrrmm... what if it's possible that the expansion will result in an
> empty string? Wouldn't quotes be the safe way to go "just in case?"

    $ v=
    $ case $v in "") echo empty;; *) echo not empty ;; esac
    empty
    $ v=in
    $ case $v in "") echo empty;; *) echo not empty ;; esac
    not empty
    $ case $v in *\ *) echo has space ;; *) echo no space ;; esac
    no space
    $ v="foo bar"
    $ case $v in *\ *) echo has space ;; *) echo no space ;; esac
    has space
    $ v="foo*bar"
    $ case $v in *\**) echo has star ;; *) echo no star ;; esac
    has star

if [[ $VAR = xyz ]]

if [[ $VAR = "$xyz" ]]

if [[ $VAR = *xyz* ]]