How to trim user input in bash script?

Question

OK, here is a given user input :

$ myscript.sh file-name.txt

I would like to trim "file-name.txt" to retrive 'file' in bash script

#!/bin/bash
FILENAME=$1

# trim text after '-' from user input 'file-name.txt'
# save 'file' back to $1

My best guess is mixing sed and regular expression somehow, but I am no expert of those :(

Any ideas?

---

I tried muru's suggestion for more complicated input.

given input : A-B-C-D-0.1.5-6.1.txt

wanted output : A-B-C-D

#!/bin/bash
TRIMMED1="${1%-*}"
TRIMMED2="${1%%-*}"
TRIMMED3="${TRIMMED1%-*}"
TRIMMED4="${TRIMMED1%%-*}"
TRIMMED5="${1%-[0-9]*}"
TRIMMED6="${1%%-[0-9]*}"
echo "user input : $1"
echo "TRIMMED1 : $TRIMMED1"
echo "TRIMMED2 : $TRIMMED2"
echo "TRIMMED3 : $TRIMMED3"
echo "TRIMMED4 : $TRIMMED4"
echo "TRIMMED5 : $TRIMMED5"
echo "TRIMMED6 : $TRIMMED6"

result:

user input : A-B-C-D-0.1.5-6.1.txt
TRIMMED1 : A-B-C-D-0.1.5
TRIMMED2 : A
TRIMMED3 : A-B-C-D
TRIMMED4 : A
TRIMMED5 : A-B-C-D-0.1.5
TRIMMED6 : A-B-C-D

Answer 1

You don't have to use external tools for this. Pure bash:

FILENAME="${1%-*}"

% is used to remove the shortest matching suffix. If you have file-name-foo, you'll get file-name. To remove the longest matching suffix, use %%.

To save to $1, you'll have to use set. Something like:

set -- "${1%-*}" "${@:2}"

Then the next time you use $1, it will have the trimmed text.

Remember, no spaces around = when assigning variables.

Answer 2

You can do it by

#!/bin/bash
FILENAME=$1
TRIMMED=$(echo "$FILENAME" | cut -f1 -d-)

The command will output field 1 using - as a delimeter.

Answer 3

Can be done like this:

#!/bin/bash
# trim text after '-' from user input 'file-name.txt'
FILENAME="$(sed 's/-.*//' <<< $1).txt"

# save 'file' back to $1
mv "$1" "$FILENAME"

Explanation:

In my example I use the sed command to shorten the name which usually has this layout 'command/search/replacement/'. In my example above i use s as command which is search and replace, then -.* as search word (regex) which will search all combinations beginning with a - then followed by a random character . and telling it this keeps on till the end with *. The replacement string I leave empty, this means file-name.txt becomes file.

The <<< is bash specific and is called a here-string, so this wont work in sh. It is like the redirections into files just that it redirects a string into the stream instead of a file.

Finaly to make the string complete I add .txt back and then do a mv to rename the file.