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Why doesn't this work: ~$ echo “trythis” | sh ./script.sh

Where I'm making the mistake in here document?Bash script to move filesWhy my shell script doesn't open the terminal?How to convert a string into an array in bash script?How can I use a pipe in a while condition?Moving files from source to destination in categoriesWhy is my bash script getting “Killed”? How do I prevent that?Bash script to create a directorymysqldump script doesn't work in cronBash script not running all comands

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

0

I'm trying to feed the string trythis into the script I made that creates a directory using what is written after it.
For example this works:

~$ sh ./script trythis

But using the pipe does not.
I am rather new to scripting so still getting the hang of various concepts.

command-line scripts pipe

share|improve this question

edited Apr 14 at 19:40

Sergiy Kolodyazhnyy

76.2k10161336

asked Apr 14 at 19:05

David David

82

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why did you expect it to work?
  
  – fkraiem
  Apr 14 at 19:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See this question
  
  – Elias
  Apr 14 at 19:09
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I was going to add to my answer whole lot of extra information about how things work behind the scenes, but considering you're somewhat new to scripting I've put that aside for now. Too much information can be overwhelming. Please let me know if you do what extra clarifications on any of the things in my answer
  
  – Sergiy Kolodyazhnyy
  Apr 14 at 19:42
  
  

  
  
  
  

add a comment | 

0

I'm trying to feed the string trythis into the script I made that creates a directory using what is written after it.
For example this works:

~$ sh ./script trythis

But using the pipe does not.
I am rather new to scripting so still getting the hang of various concepts.

command-line scripts pipe

share|improve this question

edited Apr 14 at 19:40

Sergiy Kolodyazhnyy

76.2k10161336

asked Apr 14 at 19:05

David David

82

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why did you expect it to work?
  
  – fkraiem
  Apr 14 at 19:08
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See this question
  
  – Elias
  Apr 14 at 19:09
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I was going to add to my answer whole lot of extra information about how things work behind the scenes, but considering you're somewhat new to scripting I've put that aside for now. Too much information can be overwhelming. Please let me know if you do what extra clarifications on any of the things in my answer
  
  – Sergiy Kolodyazhnyy
  Apr 14 at 19:42
  
  

  
  
  
  

add a comment | 

I'm trying to feed the string trythis into the script I made that creates a directory using what is written after it.
For example this works:

~$ sh ./script trythis

But using the pipe does not.
I am rather new to scripting so still getting the hang of various concepts.

command-line scripts pipe

share|improve this question

edited Apr 14 at 19:40

Sergiy Kolodyazhnyy

76.2k10161336

asked Apr 14 at 19:05

David David

82

~$ sh ./script trythis

share|improve this question

edited Apr 14 at 19:40

Sergiy Kolodyazhnyy

76.2k10161336

asked Apr 14 at 19:05

David David

82

share|improve this question

edited Apr 14 at 19:40

Sergiy Kolodyazhnyy

76.2k10161336

asked Apr 14 at 19:05

David David

82

edited Apr 14 at 19:40

Sergiy Kolodyazhnyy

76.2k10161336

edited Apr 14 at 19:40

Sergiy Kolodyazhnyy

76.2k10161336

asked Apr 14 at 19:05

David David

82

asked Apr 14 at 19:05

David David

82

1 Answer
1

active

oldest

votes

2

Because pipe and positional parameters are different things

Pipes connect stdin stream of right most command in pipeline to the stdout of left most command. The effect is such as if one command becomes keyboard-like input to the other.

By contrast positional parameters as in

myscript.sh trythis

create an array of values, where myscript and trythis are items in that array, and there is no connection to stdin stream at all

What you should do in such cases is use xargs

echo trythis | xargs myscript 

The xargs command will run the myscript command with trythis added to the front as if done manually.

In other words, exactly because sh ./script trythis expects trythis to be there in positional parameter list you don't see echo trythis | sh ./myscript working. If you did echo try this | sh ./myscript trythis it would work, because now you have positional parameter list, and echo technically becomes redundant.

Of course, it is the application's own decision on what to do with either stdin or positional parameters. Commands such as echo don't care about stdin but only about positional parameters, whereas cat would care about both. If you were to build a script in such way that reads stdin AND accepts positional parameters, then it could also work, for instance grep and tail do that. And exactly in those cases where we want to dynamically create positional parameters or the application ignores stdin - there is the right place to use xargs.

share|improve this answer

edited Apr 14 at 19:32

answered Apr 14 at 19:14

Sergiy KolodyazhnyySergiy Kolodyazhnyy

76.2k10161336

add a comment | 

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2

Because pipe and positional parameters are different things

Pipes connect stdin stream of right most command in pipeline to the stdout of left most command. The effect is such as if one command becomes keyboard-like input to the other.

By contrast positional parameters as in

myscript.sh trythis

create an array of values, where myscript and trythis are items in that array, and there is no connection to stdin stream at all

What you should do in such cases is use xargs

echo trythis | xargs myscript 

The xargs command will run the myscript command with trythis added to the front as if done manually.

In other words, exactly because sh ./script trythis expects trythis to be there in positional parameter list you don't see echo trythis | sh ./myscript working. If you did echo try this | sh ./myscript trythis it would work, because now you have positional parameter list, and echo technically becomes redundant.

Of course, it is the application's own decision on what to do with either stdin or positional parameters. Commands such as echo don't care about stdin but only about positional parameters, whereas cat would care about both. If you were to build a script in such way that reads stdin AND accepts positional parameters, then it could also work, for instance grep and tail do that. And exactly in those cases where we want to dynamically create positional parameters or the application ignores stdin - there is the right place to use xargs.

share|improve this answer

edited Apr 14 at 19:32

answered Apr 14 at 19:14

Sergiy KolodyazhnyySergiy Kolodyazhnyy

76.2k10161336

add a comment | 

2

Because pipe and positional parameters are different things

Pipes connect stdin stream of right most command in pipeline to the stdout of left most command. The effect is such as if one command becomes keyboard-like input to the other.

By contrast positional parameters as in

myscript.sh trythis

create an array of values, where myscript and trythis are items in that array, and there is no connection to stdin stream at all

What you should do in such cases is use xargs

echo trythis | xargs myscript 

The xargs command will run the myscript command with trythis added to the front as if done manually.

In other words, exactly because sh ./script trythis expects trythis to be there in positional parameter list you don't see echo trythis | sh ./myscript working. If you did echo try this | sh ./myscript trythis it would work, because now you have positional parameter list, and echo technically becomes redundant.

Of course, it is the application's own decision on what to do with either stdin or positional parameters. Commands such as echo don't care about stdin but only about positional parameters, whereas cat would care about both. If you were to build a script in such way that reads stdin AND accepts positional parameters, then it could also work, for instance grep and tail do that. And exactly in those cases where we want to dynamically create positional parameters or the application ignores stdin - there is the right place to use xargs.

share|improve this answer

edited Apr 14 at 19:32

answered Apr 14 at 19:14

Sergiy KolodyazhnyySergiy Kolodyazhnyy

76.2k10161336

add a comment | 

Because pipe and positional parameters are different things

Pipes connect stdin stream of right most command in pipeline to the stdout of left most command. The effect is such as if one command becomes keyboard-like input to the other.

By contrast positional parameters as in

myscript.sh trythis

create an array of values, where myscript and trythis are items in that array, and there is no connection to stdin stream at all

What you should do in such cases is use xargs

echo trythis | xargs myscript 

The xargs command will run the myscript command with trythis added to the front as if done manually.

In other words, exactly because sh ./script trythis expects trythis to be there in positional parameter list you don't see echo trythis | sh ./myscript working. If you did echo try this | sh ./myscript trythis it would work, because now you have positional parameter list, and echo technically becomes redundant.

Of course, it is the application's own decision on what to do with either stdin or positional parameters. Commands such as echo don't care about stdin but only about positional parameters, whereas cat would care about both. If you were to build a script in such way that reads stdin AND accepts positional parameters, then it could also work, for instance grep and tail do that. And exactly in those cases where we want to dynamically create positional parameters or the application ignores stdin - there is the right place to use xargs.

share|improve this answer

edited Apr 14 at 19:32

answered Apr 14 at 19:14

Sergiy KolodyazhnyySergiy Kolodyazhnyy

76.2k10161336

myscript.sh trythis

echo trythis | xargs myscript 

share|improve this answer

edited Apr 14 at 19:32

answered Apr 14 at 19:14

Sergiy KolodyazhnyySergiy Kolodyazhnyy

76.2k10161336

answered Apr 14 at 19:14

Sergiy KolodyazhnyySergiy Kolodyazhnyy

76.2k10161336

answered Apr 14 at 19:14

Sergiy KolodyazhnyySergiy Kolodyazhnyy

76.2k10161336