Bash and Variable Substitution for file with space in their name: application for gpsbabel - linux

Question

I am trying to program a script to run gpsbabel. I am stuck to handle files with name containing (white) spaces.
My problem is in the bash syntax. Any help or insight from bash programmers will be much appreciated.
gpsbabel is software which permit merging of tracks recorded by gps devices.
The syntax for my purpose and which is working is:
gpsbabel -i gpx -f "file 1.gpx" -f "file 2.gpx" -o gpx -F output.gpx -x track,merge
The input format of the GPS data is given by -i , the output format by -o.
The input data files are listed after -f, and the resulting file after -F
(ref. gpsbabel manual, see example 4.9)
I am trying to write a batch to run this syntax with a number of input file not known initially. It means that the sequence -f "name_of_the_input_file" has to be repeated for each input file passed from the batch parameters.
Here is a script working for file with no spaces in their name
#!/bin/bash
# Append multiple gpx files easily
# batch name merge_gpx.sh
# Usage:
# merge_gpx.sh track_*.gpx
gpsbabel -i gpx $(echo $* | for GPX; do echo -n " -f $GPX "; done) \
-o gpx -F appended.gpx
`
So I tried to modify this script to handle also filename with containing spaces.
I got lost in the bash substitution and wrote and more sequenced bash for debugging purpose with no success.
Here is one of my trial
I get an error from gpsbabel "Extra arguments on command line" suggesting that I made a mistake in the variable usage.
#/bin/bash
# Merging all tracks in a single one
old_IFS=$IFS # Backup internal separator
IFS=$'\n' # New IFS
let i=0
echo " Merging GPX files"
for file in $(ls -1 "$#")
do
let i++
echo "i=" $i "," "$file"
tGPX[$i]=$file
done
IFS=$old_IFS #
#
echo "Number of files:" ${#tGPX[#]}
echo
# List of the datafile to treat (each name protected with a ')
LISTE=$(for (( ifile=1; ifile<=${#tGPX[#]} ; ifile++)) ;do echo -ne " -f '""${tGPX[$ifile]}""'"; done)
echo "LISTE: " $(echo -n $LISTE)
echo "++Merging .."
if (( $i>=1 )); then
gpsbabel -t \
-i gpx $(echo -n $LISTE) \
-x track,merge,title="TEST COMPIL" \
-o gpx -F track_compil.gpx
else
echo "Wrong selection of input file"
fi
#end

Answer 1

You are making things way more complicated for yourself than they need to be.
Any reasonably posix/gnu-compatible utility which takes an option in the form of two command-line arguments (-f STRING, or equivalently -f FILENAME) should also accept a single command-line argument -fSTRING. If the utility uses either getopt or getopt_long, this is automatic. gpsbabel appears to not use standard posix or gnu libraries for argument parsing, but I believe it still gets this right.
Apparently, your script expects its arguments to be a list of filenames; presumably, if the filenames include whitespace, you will quote the names which include whitespace:
./myscript "file 1.gpx" "file 2.gpx"
In that case, you only need to change the list of arguments by prepending -f to each one, so that the argument list becomes, in effect:
"-ffile 1.gpx" "-ffile 2.gpx"
That's extremely straightforward. We'll use the bash-specific find-and-replace syntax, described in the bash manual: (I highlighted the two features this solution uses)
${parameter/pattern/string}
Pattern substitution. The pattern is expanded to produce a pattern just as in pathname expansion. Parameter is expanded and the longest match of pattern against its value is replaced with string. If pattern begins with /, all matches of pattern are replaced with string. Normally only the first match is replaced. If pattern begins with #, it must match at the beginning of the expanded value of parameter. If pattern begins with %, it must match at the end of the expanded value of parameter. If string is null, matches of pattern are deleted and the / following pattern may be omitted. If parameter is # or *, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with # or *, the substitution operation is applied to each member of the array in turn, and the expansion is the resultant list.
So, "${#/#/-f}" is the list of arguments (#), with the empty pattern at the beginning (#) replaced with -f:
#/bin/bash
# Merging all tracks in a single one
# $# is the number of arguments to the script.
if (( $# > 0 )); then
gpsbabel -t \
-i gpx "${#/#/-f}" \
-x track,merge,title="TEST COMPIL" \
-o gpx -F track_compil.gpx
else
# I changed the error message to make it more clear, sent it to stderr
# and cause the script to fail.
echo "No input files specified" >> /dev/stderr
exit 1
fi

Answer 2

Use an array:
files=()
for f; do
files+=(-f "$f")
done
gpsbabel -i gpx "${files[#]}" -o gpx -F appended.gpx
for f; do is short for for f in "$#"; do; most often you want to use $# to access the command-line arguments instead of $*. Quoting "${files[#]}" produces a list of words, one per element, that are treated as if they were quoted, so array elements containing whitespace are treated as a single word.