I have a bash script that employs the read command to read arguments to commands interactively, for example yes/no options. Is there a way to call this script in a non-interactive script passing default option values as arguments?
It's not just one option that I have to pass to the interactive script.
Many ways
pipe your input
echo "yes
no
maybe" | your_program
redirect from a file
your_program < answers.txt
use a here document (this can be very readable)
your_program << ANSWERS
yes
no
maybe
ANSWERS
use a here string
your_program <<< $'yes\nno\nmaybe\n'
For more complex tasks there is expect ( http://en.wikipedia.org/wiki/Expect ).
It basically simulates a user, you can code a script how to react to specific program outputs and related stuff.
This also works in cases like ssh that prohibits piping passwords to it.
You can put the data in a file and re-direct it like this:
$ cat file.sh
#!/bin/bash
read x
read y
echo $x
echo $y
Data for the script:
$ cat data.txt
2
3
Executing the script:
$ file.sh < data.txt
2
3
Just want to add one more way. Found it elsewhere, and is quite simple.
Say I want to pass yes for all the prompts at command line for a command "execute_command", Then I would simply pipe yes to it.
yes | execute_command
This will use yes as the answer to all yes/no prompts.
You can also use printf to pipe the input to your script.
var=val
printf "yes\nno\nmaybe\n$var\n" | ./your_script.sh
Related
I have a bash script that employs the read command to read arguments to commands interactively, for example yes/no options. Is there a way to call this script in a non-interactive script passing default option values as arguments?
It's not just one option that I have to pass to the interactive script.
Many ways
pipe your input
echo "yes
no
maybe" | your_program
redirect from a file
your_program < answers.txt
use a here document (this can be very readable)
your_program << ANSWERS
yes
no
maybe
ANSWERS
use a here string
your_program <<< $'yes\nno\nmaybe\n'
For more complex tasks there is expect ( http://en.wikipedia.org/wiki/Expect ).
It basically simulates a user, you can code a script how to react to specific program outputs and related stuff.
This also works in cases like ssh that prohibits piping passwords to it.
You can put the data in a file and re-direct it like this:
$ cat file.sh
#!/bin/bash
read x
read y
echo $x
echo $y
Data for the script:
$ cat data.txt
2
3
Executing the script:
$ file.sh < data.txt
2
3
Just want to add one more way. Found it elsewhere, and is quite simple.
Say I want to pass yes for all the prompts at command line for a command "execute_command", Then I would simply pipe yes to it.
yes | execute_command
This will use yes as the answer to all yes/no prompts.
You can also use printf to pipe the input to your script.
var=val
printf "yes\nno\nmaybe\n$var\n" | ./your_script.sh
This question already has answers here:
Passing arguments to an interactive program non-interactively
(5 answers)
Closed 7 years ago.
So suppose a normal command run in terminal goes like this....
user$ thecommand
Please enter your first name:
>
and then waits for your to type your name... straightforward, but if in a bash script I try and do something like:
#! /bin/bash
echo "What is your name?"
read name
thecommand
how would I have THE SCRIPT enter "$name" in response to "thecommand" instead of having the user manually input it themselves?
you can add input by pipe like this:
echo yourname | ./yourscript
for more inputs you can use printf
printf "input1\ninput2" | ./yourscript
where \n means new line and it will be used like new input.
Run your script like:
./yourscript.sh < file.txt
where file.txt will contain the name.
now your script will look for name from the file(file.txt), in file.txt you can type the names which will act as input for read command.
read command reads on line at a time so if u have more than on read command in your script you should have multiple lines in file.txt file
For complicated cases, for example if your input depends on the output of your command, you may write an "expect" script.
To see how it works you can auto-generate such script interactively
$ autoexpect thecommand
And then run it
$ expect -f script.exp
Hi my question is simple. I want to do this in a command prompt.
var="ls | cat"
$var
Now I know that when I try to do this manually
ls | cat
Bash takes | as a special thing. I don't know how its called, I know | it's called a pipe but I mean that bash takes | as a ... and actually makes a pipe. I also figured that when I try to do $var bash actually takes | as a string and not as a pipe. Well, my question is How can I make bash to realize that | is actually a pipe and not a string. Thanks, I hope I am clear about my point.
Simple solution: use eval:
var="ls | cat"
eval $var
bash interprets the arguments to eval as if you had typed that on the command line.
Of course, keep in mind the security risks to using eval with user input, in case that's an issue for your program.
This may or may not apply - but it sounds like you may be looking for the alias command. You can do alias var="ls | cat" and then in your command prompt you can do var and it treats it as if you wrote ls | cat
Rather than trying to embed executable code into a variable (which should be used to hold data, not code), use a shell function, which is intended to hold code:
my_func () {
ls | cat
}
| is called a pipe, I haven't heard any other naming. Basically the stream output by the command on its left goes as the input to the command on its right. In your case, ls output goes into a stream (i.e. a temporary file), and that stream is fed to cat. cat prints the content of a file, and ls stream is very much like a file.
Now, you are trying to make bash interpret your variable var. To do this, try:
var=`ls | cat`
$var
On my computer I get this:
-bash: Applications: command not found
Because in my case, $var is expanded to Applications Documents Downloads, the output of my ls.
Given crudely as is, bash believes this is a command I want him to execute.
If your intention is not to execute $varcontent but print it, try:
var=`ls | cat`
echo $var
The cat is not needed here, just use ls -1 and as other answers say you can alias it or put it in a function.
For example, if you want to override ls to print each file on a new line do something like
> alias ls='command ls -1'
> ls
file1
file2
etc...
And put it in a bash init file like ~/.bashrc if you want to make the change permanent
1) Functions are suitable for such tasks:
func (){
ls | cat
}
Invoke it by saying func
2) Also another suitable solution could be eval:
eval takes a string as its argument, and evaluates it as if you'd typed that string on a command line. (If you pass several arguments, they are first joined with spaces between them.)
var="ls | cat"
eval $var
I want to write several lines (5 or more) to a file I'm going to create in script. I can do this by echo >> filename. But I would like to know what the best way to do this?
You can use a here document:
cat <<EOF >> outputfile
some lines
of text
EOF
I usually use the so-called "here-document" Dennis suggested. An alternative is:
(echo first line; echo second line) >> outputfile
This should have comparable performance in bash, as (....) starts a subshell, but echo is 'inlined' - bash does not run /bin/echo, but does the echo by itself.
It might even be faster because it involves no exec().
This style is even more useful if you want to use output from another command somewhere in the text.
I'm trying to automate a proces which I have to do over and over again in which I have to parse the output from a shell function, look for 5 different things, and then put them on a file
I know I can match patterns with grep however I don't know how to store the result on a variable so I can use it after :(
I also have to parse this very same output to get the other 5 values
I have no idea on how to use the same output for the 5 grep's i need to do and then store it to 5 different variables for after use
I know i have to create a nice and tidy .sh but I don't know how to do this
Currently im trying this
#!/bin/bash
data=$(cat file)
lol=$(echo data|grep red)
echo $lol
not working , any ideas?
you should show some examples of what you want to do next time..
assuming you shell function is called func1
func1(){
echo "things i want to get are here"
}
func1 | grep -E "things|want|are|here|get" > outputfile.txt
Update:
your code
#!/bin/bash
data=$(cat file)
lol=$(echo data|grep red)
echo $lol
practically just means this
lol=$(grep "red" file)
or
lol=$(awk '/red/' file)
also, if you are considering using bash, this is one way you can do it
while read -r myline
do
case "$myline" in
*"red"* ) echo "$myline" >> output.txt
esac
done <file
You can use the following syntax:
VAR=$(grep foo bar)
or alternatively:
VAR=`grep foo bar`
The easiest thing to do would be to redirect the output of the function to a file. You can then run multiple greps on it and only delete the file once you are done with it.
To save the output, you want to use command substitution. This runs a command and then converts the output into command line parameter. Combined with variable assignment you get:
variable=$(grep expression file)
Your second line is wrong. Change it to this:
lol=$(echo "$data"|grep red)
use egrep istead of grep.
variable=$(egrep "exp1|exp2|exp3|exp4|exp5" file)