[BASH] tilde doesn't expand from user input?

[gandalf3]

I am learning some bash scripting, and I want to have the user type in a path to some directory and allow the use of ~
so that

echo 'type path to somedir'
read -e -p "> " path
path=${path//\~/$HOME}
echo 'your path:'
echo $path
however, it seems the tilde charecter cannot be replaced??

EDIT:
fixed code, thanks.

[schragge]

Try

path=${path/#\~/$HOME} Actually, there's not much point in such substitution as you can force tilde expansion with eval: Edit. Too dangerous, see Vaphell's post below.


read -ep 'type path to somedir ' path
eval echo your path: $path

Moreover, tilde not always expands to $HOME. E.g. ~user means home directory of user, ~+ = $PWD, ~- = $OLDPWD, and so on.

Note also that your code has other problems, too: no prompt after read -p and single quotes in the last line (shell parameters get expanded only inside double quotes).

[gandalf3]

Try
Code:

path=${path/#\~/$HOME}
oh wow that worked! thanks.
thanks for the tip about eval, i think i'll use that.
though i can't get the variable path reassigend to the eval-ifide path??



read -ep '> ' path
path= eval echo $path
echo $path


EDIT


i can't mark as solved in "thread tools"??

im not used to the new interface yet.. probably just me being an idiot :oops:

[schragge]

i can't mark as solved in "thread tools"??You need to edit the thread name manually as described in this post.

[Vaphell]

for gods sake never eval user input.

what if someone types

; rm -rf ~
?

stick to ${path/#\~/$HOME}

[schragge]

:oops: You are right. Then maybe do it like this:


IFS=';&|()`'
read -ep '> ' path junk
path=$(eval echo $path)
echo $path
:?: I see why this is suboptimal and rather fragile as it would break on paths containing characters listed in $IFS, but at least the full semantics of ~ would be preserved.

Update.
After giving it some more thought, now I guess the most prudent way would be using the case statement:


#!/bin/sh
LC_ALL=C # for [a-z] to work as expected
test -n "$1" && path=$1 || read -p '> ' path
case $path in ~*)
pfx=${path%%/*}; tag=${pfx#\~}; tail=${path#$pfx}
case $tag in
'') path=$HOME$tail;;
+) path=$PWD$tail;;
-) test -n "$OLDPWD" && path=$OLDPWD$tail;;
[a-z_]*) passwd=`getent passwd "$tag"` && pfx=${passwd%:*}&&path=${pfx##*:}$tail;;
# Some custom shortcuts
DC) path=$HOME/Documents$tail;;
DL) path=$HOME/Downloads$tail;;
DT) path=$HOME/Desktop$tail;;
ML) path=$HOME/Mail$tail;;
MU) path=$HOME/Music$tail;;
PC) path=$HOME/Pictures$tail;;
PB) path=$HOME/Public$tail;;
TL) path=$HOME/Templates$tail;;
VD) path=$HOME/Videos$tail;;
CF) path=$HOME/.config$tail;;
LC) path=$HOME/.local/share$tail;;
MD) path=/media$tail;;
esac
esac
echo $path

The same in bash


#!/bin/bash
LC_ALL=C # for [a-z] to work as expected
shopt -s extglob # for $DIRSTACK
declare -A shortcuts
shortcuts=(
[DC]=Documents [DL]=Downloads [DT]=Desktop [ML]=Mail [MU]=Music
[PC]=Pictures [PB]=Public [TL]=Templates [VD]=Videos [CF]=.config
[LC]=.local/share
)
[[ -n $1 ]] path=$1 || read -ep '> ' path
if [[ $path == ~* ]]; then
pfx=${path%%/*}; tag=${pfx:1}; tail=${path#$pfx}
case $tag in
'') path=$HOME$tail;;
+) path=$PWD$tail;;
-) [[ -n $OLDPWD ]] && path=$OLDPWD$tail;;
?(+|-)+([0-9])) path=${DIRSTACK[$tag]}$tail;;
DC|DL|DT|MU|PC|PB|TL|VD|CF|LC) path=$HOME/${shortcuts[$tag]}$tail};;
MD) path=/media$tail;;
[a-z_]*) ifs=$IFS;IFS=:; passwd=(`getent passwd "$tag"`)&&path=${passwd[5]}$tail; IFS=$ifs;;
esac
fi
echo $path

[gandalf3]

:shock: That is a LOT of stuff... for something as seemingly simple as makeing "~" work in the read command..
(i see the problem though.. there seems like there ought to be some way to eval just the tilde?)

im currantly sticking to



path=${path//\~/$HOME}

because it's in a situation where the user is unlikely to use ~ for anything other than $HOME..
good to know though, i'll keep it in mind for future use..

EDIT:

wow
I didn't realize bash and sh were that different!

[Vaphell]

sh is more suited for barebone stuff, like running system scripts that are relatively simple and using bash on them would just waste resources. Bash offers goodies that are more useful in userspace scripts. Some people even think bash is bloated ;-)

path=${path/#\~/$HOME} should be good enough in most cases (# forces the pattern to match from the left so eg file~ wont get a substitution). If you think user can have a file with ~filename, you could try doing a test if the file/dir with that exact name exists. If not, assume he meant $HOME and do a replacement, eg

[ -e "$path" ] || path=${path/#\~/$HOME}

[gandalf3]

I found that it was just easer to do without the read command, instead have a command line argument. now the shell just expands it automatically before the script even gets a hold of it :) thanks