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-rw-r--r--bash.html.markdown93
1 files changed, 92 insertions, 1 deletions
diff --git a/bash.html.markdown b/bash.html.markdown
index bd2d5984..14366e4c 100644
--- a/bash.html.markdown
+++ b/bash.html.markdown
@@ -11,6 +11,10 @@ contributors:
- ["Rahil Momin", "https://github.com/iamrahil"]
- ["Gregrory Kielian", "https://github.com/gskielian"]
- ["Etan Reisner", "https://github.com/deryni"]
+ - ["Jonathan Wang", "https://github.com/Jonathansw"]
+ - ["Leo Rudberg", "https://github.com/LOZORD"]
+ - ["Betsy Lorton", "https://github.com/schbetsy"]
+ - ["John Detter", "https://github.com/jdetter"]
filename: LearnBash.sh
---
@@ -54,6 +58,13 @@ echo '$Variable'
# its name without $. If you want to use the variable's value, you should use $.
# Note that ' (single quote) won't expand the variables!
+# Parameter expansion ${ }:
+echo ${Variable}
+# This is a simple usage of parameter expansion
+# Parameter Expansion gets a value from a variable. It "expands" or prints the value
+# During the expansion time the value or parameter are able to be modified
+# Below are other modifications that add onto this expansion
+
# String substitution in variables
echo ${Variable/Some/A}
# This will substitute the first occurrence of "Some" with "A"
@@ -68,6 +79,12 @@ echo ${Foo:-"DefaultValueIfFooIsMissingOrEmpty"}
# This works for null (Foo=) and empty string (Foo=""); zero (Foo=0) returns 0.
# Note that it only returns default value and doesn't change variable value.
+# Brace Expansion { }
+# Used to generate arbitrary strings
+echo {1..10}
+echo {a..z}
+# This will output the range from the start value to the end value
+
# Builtin variables:
# There are some useful builtin variables, like
echo "Last program's return value: $?"
@@ -76,6 +93,21 @@ echo "Number of arguments passed to script: $#"
echo "All arguments passed to script: $@"
echo "Script's arguments separated into different variables: $1 $2..."
+# Now that we know how to echo and use variables,
+# let's learn some of the other basics of bash!
+
+# Our current directory is available through the command `pwd`.
+# `pwd` stands for "print working directory".
+# We can also use the builtin variable `$PWD`.
+# Observe that the following are equivalent:
+echo "I'm in $(pwd)" # execs `pwd` and interpolates output
+echo "I'm in $PWD" # interpolates the variable
+
+# If you get too much output in your terminal, or from a script, the command
+# `clear` clears your screen
+clear
+# Ctrl-L also works for clearing output
+
# Reading a value from input:
echo "What's your name?"
read Name # Note that we didn't need to declare a new variable
@@ -124,12 +156,54 @@ ls
# These commands have options that control their execution:
ls -l # Lists every file and directory on a separate line
+ls -t # Sorts the directory contents by last-modified date (descending)
+ls -R # Recursively `ls` this directory and all of its subdirectories
# Results of the previous command can be passed to the next command as input.
# grep command filters the input with provided patterns. That's how we can list
# .txt files in the current directory:
ls -l | grep "\.txt"
+# Use `cat` to print files to stdout:
+cat file.txt
+
+# We can also read the file using `cat`:
+Contents=$(cat file.txt)
+echo "START OF FILE\n$Contents\nEND OF FILE"
+
+# Use `cp` to copy files or directories from one place to another.
+# `cp` creates NEW versions of the sources,
+# so editing the copy won't affect the original (and vice versa).
+# Note that it will overwrite the destination if it already exists.
+cp srcFile.txt clone.txt
+cp -r srcDirectory/ dst/ # recursively copy
+
+# Look into `scp` or `sftp` if you plan on exchanging files between computers.
+# `scp` behaves very similarly to `cp`.
+# `sftp` is more interactive.
+
+# Use `mv` to move files or directories from one place to another.
+# `mv` is similar to `cp`, but it deletes the source.
+# `mv` is also useful for renaming files!
+mv s0urc3.txt dst.txt # sorry, l33t hackers...
+
+# Since bash works in the context of a current directory, you might want to
+# run your command in some other directory. We have cd for changing location:
+cd ~ # change 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??
+
+# Use subshells to work across directories
+(echo "First, I'm here: $PWD") && (cd someDir; echo "Then, I'm here: $PWD")
+pwd # still in first directory
+
+# Use `mkdir` to create new directories.
+mkdir myNewDir
+# The `-p` flag causes new intermediate directories to be created as necessary.
+mkdir -p myNewDir/with/intermediate/directories
+
# You can redirect command input and output (stdin, stdout, and stderr).
# Read from stdin until ^EOF$ and overwrite hello.py with the lines
# between "EOF":
@@ -168,7 +242,9 @@ echo "#helloworld" | cat > output.out
echo "#helloworld" | tee output.out >/dev/null
# Cleanup temporary files verbosely (add '-i' for interactive)
+# WARNING: `rm` commands cannot be undone
rm -v output.out error.err output-and-error.log
+rm -r tempDir/ # recursively delete
# Commands can be substituted within other commands using $( ):
# The following command displays the number of files and directories in the
@@ -259,10 +335,25 @@ sed -i 's/okay/great/g' file.txt
grep "^foo.*bar$" file.txt
# pass the option "-c" to instead print the number of lines matching the regex
grep -c "^foo.*bar$" file.txt
+# Other useful options are:
+grep -r "^foo.*bar$" someDir/ # recursively `grep`
+grep -n "^foo.*bar$" file.txt # give line numbers
+grep -rI "^foo.*bar$" someDir/ # recursively `grep`, but ignore binary files
+# perform the same initial search, but filter out the lines containing "baz"
+grep "^foo.*bar$" file.txt | grep -v "baz"
+
# if you literally want to search for the string,
# and not the regex, use fgrep (or grep -F)
-fgrep "^foo.*bar$" file.txt
+fgrep "foobar" file.txt
+
+# trap command allows you to execute a command when a signal is received by your script.
+# Here trap command will execute rm if any one of the three listed signals is received.
+trap "rm $TEMP_FILE; exit" SIGHUP SIGINT SIGTERM
+# `sudo` is used to perform commands as the superuser
+NAME1=$(whoami)
+NAME2=$(sudo whoami)
+echo "Was $NAME1, then became more powerful $NAME2"
# Read Bash shell builtins documentation with the bash 'help' builtin:
help