See the cheatsheet on regular expressions for more "wildcard" shortcuts.
### b) How to redirect to a file and get input from a file ...
+Redirection operators can be used to redirect the ouput from a program from the display screen to a file where it is saved (or many other places too, like your printer or to another program where it can be used as input).
-#### Definitions:
-* **stdout**:
-* **stdin**:
-* **stderr**:
-| Command | Description |
-|---------|-------------|
-| `>` |
-| `>>` |
-| `<` |
-| `<<` |
+| Command | Description |
+|---------|---------------------------------------------------------------------------------------------------------------------------------|
+| `>` | write `stdout` to a new file; overwrites any file with that name (e.g., `ls *.md > mardkownfiles.txt`) |
+| `>>` | append `stdout` to a previously existing file; if the file does not exist, it is created (e.g., `ls *.md >> markdownfiles.txt`) |
+| `<` | assigns the information in a file to a variable, loop, etc (e.g., `n < markdownfiles.md`) |
-### e) How to use the output of one command as the input to another with a pipe...
-### f) That combining single-purpose filters with pipes is the most productive way to use the shell...
-### g) That if a program conforms to Unix conventions, it can easily be combined with others...
+#### b.1) How to use the output of one command as the input to another with a pipe...
+A special kind of redirection is called a pipe and is denoted by `|`.
-## 4. Variables
-### a) Assignment
-* **`varname=1`** -->
-### b) Indexing
-* **`varname[0]`** --> _Note:_ the shell is zero indexed. That means you always start counting from zero
+| Command | Description |
+|---------|-------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `|` | Output from one command line program can be used as input to another one (e.g. `ls *.md | head` gives you the first 5 `*.md` files in your directory) |
+
+
+
+
+##### Example:
+
+ ls *.md | head | sed -i `s/markdown/software/g`
+
+changes all the instances of the word `markdown` to `software` in the first 5 `*.md` files in your current directory.
-### c) Referencing
-* **`${varname}` -->
-* **`${varname[@]` -->
-## 5. Loops
-NEED TO DO VARIABLE ASSIGNMENT FIRST!!!!
-### a) How to repeat operations using a loop...
-* **`for`** -->
- `for filename in *.dat
+## 4. How to repeat operations using a loop...
+Loops assign a value in a list or counter to a variable that takes on a different value each time through the loop.
+There are 2 primary kinds of loops: `for` loops and `while` loops.
+
+### a) For loop
+For loops loop through variables in a list
+
+
+ for varname in list
do
- mv ${filename} ${newname}
- done`
+ command 1
+ command 2
+ done
+
+where,
+
+* `for`, `in`, `do`, and `done` are keywords
+* `list` contains a list of values separated by spaces. e.g. `list` can be replaced by `1 2 3 4 5 6` or by `Bob Mary Sue Greg`. `list` can also be a variable:
+
+--
+
+ list[0]=Sam
+ list[1]=Lynne
+ list[2]=Dhavide
+ list[3]=Trevor
+ .
+ .
+ .
+ list[n]=Mark
-* **`while`** -->
- `count=0
- while ${count} -lte 6
- do
- COMMAND HERE
- done`
+which is referenced in the loop by:
-### b) That the loop variable takes on a different value each time through the loop...
-### c) The difference between a variable's name and its value...
-### d) Why spaces and some punctuation characters shouldn't be used in files' names...
-### e) How to display history and re-use commands...
-* **`history`** --> displays your command history to the standard output (usually the screen)
+ for varname in ${list[@]}
+ do
+ command 1
+ command 2
+ done
+_Note:_ Bash is zero indexed, so counting always starts at `0`, not `1`.
+
+
+### b) While Loop
+While loops loop through the commands until a condition is met. For example
+
+ COUNTER=0
+ while [ ${COUNTER} -lt 10 ]; do
+ command 1
+ command 2
+ COUNTER=`expr ${COUNTER} + 1`
+ done
+
+continues the loop as long as the value in the variable COUNTER is less than 10 (incremented by 1 on each iteration of the loop).
+
+* `while`, `do`, and `done` are keywords
+
-## 6. Shell Scripts
-### a) How to store shell commands in a file...
-### b) How to run a shell script...
-### c) How to pass filenames into a shell script...
+#### b.1) Commonly used conditional operators
+| Operator | Definition |
+|----------|--------------------------|
+| `-eq` | is equal to |
+| `-ne` | is not equal to |
+| `-gt` | greater than |
+| `-ge` | greater than or equal to |
+| `-lt` | less than |
+| `-le` | less than or equal to |
-## 7. Finding Things
+
+
+
+## 6. Finding Things
### a) How to select lines matching patterns in text files...
-* **`grep [options] day haiku.txt`** --> finds every instance of the string `day` in the file haiku.txt and pipes it to standard output.
- * **`-E`** --> tells grep you will be using a regular expression. Enclose the regular expression in quotes. _Note:_ the power of `grep` comes from using regular expressions. Please see the regular expressions sheet for examples
+
+| Example command | Description |
+|-----------------|-------------|
+| `grep [options] day haiku.txt` | finds every instance of the string `day` in the file haiku.txt and pipes it to standard output |
+| * `-E` | tells grep you will be using a regular expression. Enclose the regular expression in quotes. _Note:_ the power of `grep` comes from using regular expressions. Please see the regular expressions sheet for examples |
+
+
* **`-i`** --> makes matching case-insensitive
* **`-n`** --> limits the number of lines that match to the first n matches
* **`-v`** --> shows lines that do not match the pattern (inverts the match)
projects / swc-modular-shell.git / blobdiff