Why the pipe command "l | grep "1" " get the wrong result?

First of all, what you're trying to do , l| grep <filename> is bad. Don't do it. Here's why.

l command is really an alias to ls -CF

$ type -a l
l is aliased to `ls -CF'

By default in Ubuntu's bash , ls is an alias to ls --color=auto. As steeldriver pointed out in the comments --color=auto is supposed to turn off colorization. In your specific case , you have alias ls="ls -alh --color" and alias l="ls -CF" , which basically ends up being ls -alh --color -CF. This particular combination of switches still sends colorized output over a pipe. For example:

$ ls -alh --color -CF ~/TESTDIR | cat -A                                                                                 
^[[0m^[[01;34m.^[[0m/  ^[[01;34m..^[[0m/  1.txt  2.txt  3.txt  out.txt$

Notice how the . and .. directories have same escape sequences.

What does this all mean

This means that l will output colorized list of files according to file type. Problem is that colorization happens with the use of escape sequences. That's what 1:34m things are - they're escape sequence for specific colors.

The main problem is that parsing ls often leads to wrong output and disasters in scripts, simply because ls allows escape sequences like explained earlier and other special characters. See this article for more info: http://mywiki.wooledge.org/ParsingLs

What you should be doing:

Use find command :

bash-4.3$ ls
1.txt  2.txt  3.txt  out.txt
bash-4.3$ find . -maxdepth 1 -iname "*1*"
./1.txt

You could do something like this with shell glob and modern test [[ command:

bash-4.3$ for file in * ;do if [[ "$file" =~ "1"  ]] ;then echo "$file" ;fi ; done
1.txt

Or maybe use python, which has far better filename handling capabilities than bash alone

bash-4.3$ python -c 'import os;print [f for f in os.listdir(".") if "1" in f ]'
['1.txt']

If there's no need to process the output of ls , simple globbing with ls can do the work, too. ( Remember, this is only for viewing list of files, not for passing it to another program to deal with the output text)

bash-4.3$ ls *1*
1.txt

Your l and ls commands are setup as aliases.

When you run them piping the output through grep "1" (using |) each screen line where 1 appears is displayed, with the 1 colored red.

Because file names ., .., 2 and 22 appear on the same screen line, they are output by grep as well but do not appear in red which shows grep matches.

The :34m is an escape sequence for a color that doesn't paint properly. Based on your revised question with the output of type -a l and type -a it can be reproduced in my system. Please note you should change your alias from --color to --color=auto:

Color output