I am trying to build shell script. One of the commands used in this script is supposedly using read command demanding param to complete its execution. Now i want to pass same argument everytime for this. Can i automate this ?
In short, how to automate read command by shell script ?
Because of some reasons i can not share actual script.
If read is reading from standard input, you can just redirect from a file containing the necessary data:
$ cat foo.txt
a
b
$ someScript.sh < foo.txt
or pipe the data from another command:
$ printf 'a\nb\n' | someScript.sh
Related
I have a simple Bash script:
#!/usr/bin/env bash
read X
echo "X=$X"
When I execute it with ./myscript.sh it works. But when I execute it with cat myscript.sh | bash it actually puts echo "X=$X" into $X.
So this script prints Hello World executed with cat myscript.sh | bash:
#!/usr/bin/env bash
read X
hello world
echo "$X"
What's the benefit of executing a script with cat myscript.sh | bash? Why doesn't do it the same things as if I execute it with ./myscript.sh?
How can I avoid Bash to execute line by line but execute all lines after the STDIN reached the end?
Instead of just running
read X
...instead replace it with...
read X </dev/tty || {
X="some default because we can't read from the TTY here"
}
...if you want to read from the console. Of course, this only works if you have a /dev/tty, but if you wanted to do something robust, you wouldn't be piping from curl into a shell. :)
Another alternative, of course, is to pass in your value of X on the command line.
curl https://some.place/with-untrusted-code-only-idiots-will-run-without-reading \
| bash -s "value of X here"
...and refer to "$1" in your script when you want X.
(By the way, I sure hope you're at least using SSL for this, rather than advising people to run code they download over plain HTTP with no out-of-band validation step. Lots of people do it, sure, but that's making sites they download from -- like rvm.io -- big targets. Big, easy-to-man-in-the-middle-or-DNS-hijack targets).
When you cat a script to bash the code to execute is coming from standard input.
Where does read read from? That's right also standard input. This is why you can cat input to programs that take standard input (like sed, awk, etc.).
So you are not running "a script" per-se when you do this. You are running a series of input lines.
Where would you like read to read data from in this setup?
You can manually do that (if you can define such a place). Alternatively you can stop running your script like this.
I am using simple script to print the arguments. But not able to do so.
i am using cat command to add content to a file.
[root#cen06gst ~]# cat<<EOF>pass.sh
echo " you have passed me" $#
> EOF
But when i am seeing the file content again using cat , this is showing
[root#cen06gst ~]# cat pass.sh
echo " you have passed me"
Cat only is a command line tool to concatenate and print to the screen, it doesn't modify the file. Read
man cat
If you want to run your script, run
./pass.sh argument
It is also good practice to start your script with a shebang:
#!/bin/bash
Without it the system doesn't know what language to use to process the script.
I have a command command that takes an input file as argument. Is there a way to call command without actually creating a file?
I would like to achieve the following behavior
$ echo "content" > tempfile
$ command tempfile
$ rm tempfile
if possible:
as a one-liner,
without creating a file,
using either a bash (or sh) feature or a "well-known" command (as standard as xargs)
It feels like there must be an easy way to do it but I can't find it.
Just use a process substitution.
command <(echo "content")
Bash will create a FIFO or other type of temporary file in /dev for the standard output of whatever happens in the process. For example:
$ echo <(echo hi)
/dev/fd/63
I have a simple Bash script:
#!/usr/bin/env bash
read X
echo "X=$X"
When I execute it with ./myscript.sh it works. But when I execute it with cat myscript.sh | bash it actually puts echo "X=$X" into $X.
So this script prints Hello World executed with cat myscript.sh | bash:
#!/usr/bin/env bash
read X
hello world
echo "$X"
What's the benefit of executing a script with cat myscript.sh | bash? Why doesn't do it the same things as if I execute it with ./myscript.sh?
How can I avoid Bash to execute line by line but execute all lines after the STDIN reached the end?
Instead of just running
read X
...instead replace it with...
read X </dev/tty || {
X="some default because we can't read from the TTY here"
}
...if you want to read from the console. Of course, this only works if you have a /dev/tty, but if you wanted to do something robust, you wouldn't be piping from curl into a shell. :)
Another alternative, of course, is to pass in your value of X on the command line.
curl https://some.place/with-untrusted-code-only-idiots-will-run-without-reading \
| bash -s "value of X here"
...and refer to "$1" in your script when you want X.
(By the way, I sure hope you're at least using SSL for this, rather than advising people to run code they download over plain HTTP with no out-of-band validation step. Lots of people do it, sure, but that's making sites they download from -- like rvm.io -- big targets. Big, easy-to-man-in-the-middle-or-DNS-hijack targets).
When you cat a script to bash the code to execute is coming from standard input.
Where does read read from? That's right also standard input. This is why you can cat input to programs that take standard input (like sed, awk, etc.).
So you are not running "a script" per-se when you do this. You are running a series of input lines.
Where would you like read to read data from in this setup?
You can manually do that (if you can define such a place). Alternatively you can stop running your script like this.
I am trying to read contents of a file given from standard input into a script. Any ideas how to do that?
Basically what I want is:
someScript.ksh < textFile.txt
Inside the ksh, I am using a binary which will read data from "textFile.txt" if the file is given on the standard input.
Any ideas how do I "pass" the contents of the given input file, if any, to another binary inside the script?
You haven't really given us enough information to answer the question, but here are a few ideas.
If you have a script that you want to accept data on stdin, and that script calls something else that expects data to be passed in as a filename on the command line, you can take stdin and dump it to a temporary file. Something like:
#!/bin/sh
tmpfile=$(mktemp tmpXXXXXX)
cat > $tmpfile
/some/other/command $tmpfile
rm -f $tmpfile
(In practice, you would probably use trap to clean up the temporary file on exit).
If instead the script is calling another command that also expects input on stdin, you don't really have to do anything special. Inside your script, stdin of anything you call will be connected to stdin of the calling script, and as long as you haven't previously consumed the input you should be all set.
E.g., given a script like this:
#!/bin/sh
sed s/hello/goodbye/
I can run:
echo hello world | sh myscript.sh
And get:
goodbye world