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linuxbashshellunixpipeline

Does the pipeline modify the separator of words?

I have a confusion about pipeline operation. E.g.: 

# ls *.cfg
anaconda-ks.cfg  initial-setup-ks.cfg
# ls *.cfg | cat
anaconda-ks.cfg
initial-setup-ks.cfg

When executing ls operation only, it displays items separated by blank space (or tab): 

anaconda-ks.cfg  initial-setup-ks.cfg

But through the pipeline, it seems the space is replaced by the new line: 

anaconda-ks.cfg
initial-setup-ks.cfg

How to understand it? Is it the pipeline that modify the separator?

Solution

  • The man page for ls gives you your answer:

    If standard output is a terminal, the output is in columns (sorted vertically) and control characters are output as question marks; otherwise, the output is listed one per line and control characters are output as-is.

    When piping to another command, your output is not a terminal (i.e. an interactive login session.)