Bash Shell Command Line – How to Pass the Output of One Command as the Command-Line Argument to Another

bashcommand lineshell

So I have a script that, when I give it two addresses, will search two HTML links:

echo "http://maps.google.be/maps?saddr\=$1\&daddr\=$2" | sed 's/ /%/g'

I want to send this to wget and then save the output in a file called temp.html. I tried this, but it doesn't work. Can someone explain why and/or give me a solution please?

#!/bin/bash
url = echo "http://maps.google.be/maps?saddr\=$1\&daddr\=$2" |  sed 's/ /%/g'
wget $url

Best Answer

You can use backticks (`) to evaluate a command and substitute in the command's output, like:

echo "Number of files in this directory: `ls | wc -l`"

In your case:

wget `echo http://maps.google.be/maps?saddr\=$1\&daddr\=$2 | sed 's/ /%/g'`

Related Solutions

Bash – How to pass output of one command as an argument to another

First, you need to massage the git branch output into a useable format

$ git branch
  experiment
* master
  new feature

$ git branch | awk '/^\* / { print $2 }'
master

Now, you want to use that as an argument:

$ git pull --rebase origin $(git branch | awk '/^\* / { print $2 }')

(or you can use backticks as in psusi's answer).

This should be ok, the awk command should always match exactly one line, and I'm assuming you can't have spaces in branch names. For anything much more complicated, I'd probably wrap it into a function (or a script) so you can do some sanity checking on the intermediate values.

Bash Command-Line – How to Start Line with Command from Output of Another Command

The right thing to do here is to set up bash to prompt for installation, as explained in SamK's answer. I'll answer strictly from a shell usage perspective.

First, the text you're trying to grab is on the command's standard error, but a pipe redirects the standard output, so you need to redirect stderr to stdout.

htop 2>&1 | tail -1

To use the output of a command as part of a command line, use command substitution.

$(htop 2>&1 | tail -1)

The result of the command substitution is split into words and each word is interpreted as a wildcard pattern. Here this happens to do the right thing: this is a command line with words separated by spaces, and there are no wildcard characters.

To evaluate a string as a shell command, use eval. To treat the result of the command as a string rather than a list of wildcard patterns, put it in double quotes.

eval "$(htop 2>&1 | tail -1)"

Of course, before evaluating a shell command like that, make sure it's really what you want to execute.

Best Answer

Related Solutions

Bash – How to pass output of one command as an argument to another

Bash Command-Line – How to Start Line with Command from Output of Another Command

Related Question