diff options
| -rw-r--r-- | bash.html.markdown | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index d7d7d584..8fdfdf08 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -234,7 +234,8 @@ ls -l # Lists every file and directory on a separate line ls -t # Sorts the directory contents by last-modified date (descending) ls -R # Recursively `ls` this directory and all of its subdirectories -# Results of the previous command can be passed to the next command as input. +# Results (stdout) of the previous command can be passed as input (stdin) to the next command +# using a pipe |. Commands chained in this way are called a "pipeline", and are run concurrently. # The `grep` command filters the input with provided patterns. # That's how we can list .txt files in the current directory: ls -l | grep "\.txt" @@ -274,7 +275,7 @@ cd # also goes to home directory cd .. # go up one directory # (^^say, from /home/username/Downloads to /home/username) cd /home/username/Documents # change to specified directory -cd ~/Documents/.. # still in home directory..isn't it?? +cd ~/Documents/.. # now in home directory (if ~/Documents exists) cd - # change to last directory # => /home/username/Documents @@ -289,9 +290,13 @@ mkdir -p myNewDir/with/intermediate/directories # if the intermediate directories didn't already exist, running the above # command without the `-p` flag would return an error -# You can redirect command input and output (stdin, stdout, and stderr). +# You can redirect command input and output (stdin, stdout, and stderr) +# using "redirection operators". Unlike a pipe, which passes output to a command, +# a redirection operator has a command's input come from a file or stream, or +# sends its output to a file or stream. + # Read from stdin until ^EOF$ and overwrite hello.py with the lines -# between "EOF": +# between "EOF" (which are called a "here document"): cat > hello.py << EOF #!/usr/bin/env python from __future__ import print_function @@ -313,6 +318,8 @@ python hello.py 2> "error.err" # redirect error output to error.err python hello.py > "output-and-error.log" 2>&1 # redirect both output and errors to output-and-error.log +# &1 means file descriptor 1 (stdout), so 2>&1 redirects stderr (2) to the current +# destination of stdout (1), which has been redirected to output-and-error.log. python hello.py > /dev/null 2>&1 # redirect all output and errors to the black hole, /dev/null, i.e., no output |