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How ls | wc -l works?

 
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# 1  
Old 04-11-2008
How ls | wc -l works?
ls displays files in tabbed output. Say a directory contains 3 files. ls will list all 3 in one line. So, I expect ls | wc -l to give 1, but it counts the nr of files and gives 3.

Can someone explain how this works?
# 2  
Old 04-11-2008
Hint: ls | cat

It displays differently when it's connected to a terminal (human-readable) than when it's not (machine-readable). This is a feature, but it can be a problem, too.
# 3  
Old 04-11-2008
oh, yes! Thanks for the clarification.
# 4  
Old 04-11-2008
Hammer & Screwdriver
From the manpage:
Code:
     There are three major listing formats.  The  default  format
     for  output  directed  to  a  terminal  is multi-column with
     entries sorted down the columns. The -1 option allows single
     column  output and -m enables stream output format. In order
     to determine output formats for the -C, -x, and -m  options,
     ls  uses  an environment variable, COLUMNS, to determine the
     number of character positions available on one output  line.
     If  this  variable  is  not set, the terminfo(4) database is
     used to determine  the  number  of  columns,  based  on  the
     environment  variable,  TERM.  If this information cannot be
     obtained, 80 columns are assumed.

What you are seeing in your example
> ls | wc -l
> 3

is related to the number of columns that can be displayed.
whap is happening is similar to
> ls -1 | wc -l
> 3

and here, the output was forced to just one column
 
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