Script redirect command output to last filename argument

Question

File name:Tree(executable)

#!/bin/bash
for i in $*
do
    if [ -d $i ]; then

        echo "===================$i================" >> ????? 
        tree -L 1 $i >> ?????
    fi
done

As you see, I want to list the tree structure of the parameters that I input,I want to let all the tree structure redirect to the last file(it's id is $#),it is "?????" in this script,because I do not know how to write it.

For example:

./Tree ./* README

YES,all directory tree structure will write in README!

You could just write to stdout and let the user redirect wherever they want: ./Tree ./* > README. That way they could view the output on screen or pipe it to less or what have you. — John Kugelman
– John Kugelman, Commented Oct 21, 2015 at 18:04

Etan Reisner · Accepted Answer · 2015-10-21 18:06:38Z

3

It would be easier/simpler to do this if your output file was the first argument instead of the last.

That would just need

output=$1
shift

added to the top of the script.

Using the last argument isn't harder really it just involves more "advanced" variable usage:

#!/bin/bash
output="${@: -1}"

for i in "${@:0:${#@}}"
do
    if [ -d "$i" ]; then

        echo "===================$i================" >> "$output"
        tree -L 1 "$i" >> "$output"
    fi
done

Where "${@: -1}" is the last element in the array of arguments and "${@:0:${#@}}" is the arguments from 0 to ${#@} (the length of $@ which is the count of arguments to the script).

answered Oct 21, 2015 at 18:06

Etan Reisner

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Comments

chepner · Accepted Answer · 2015-10-21 18:08:01Z

2

It would be better to put the name of the output file first, so that it doesn't interfere with the variable-length list of files you iterate over:

#!/bin/bash
output=$1
shift

for i in "$@"; 
do
    if [ -d "$i" ]; then

        echo "===================$i================" 
        tree -L 1 "$i"
    fi
done > "$output"

Then call your script as

./Tree README ./*

Better yet, there's really no need to pass the name of the output file to the script; just let the script write to standard output and do the redirection outside.

./Tree ./* > README

edited Oct 21, 2015 at 18:08

answered Oct 21, 2015 at 18:04

chepner

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2 Comments

Etan Reisner Over a year ago

You should probably advise using "$@" and "$i".

Zhang Tao Over a year ago

If I just only want to put the output file in the last ,What should I do?

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