notes update

src/rhcsa.md

@@ -1207,3 +1207,162 @@ ls -l > output.txt
 ### redirect the output of the ls command to a file and append to the file
 ls -l >> output.txt
 ```
+
+### Appending Output and Standard Error
+```bash
+### 1> redirects the output to a file
+### 2> redirects the error to a file
+
+### redirect the output of the ls command to a file and append to the file
+ls -l >> output.txt 2>&1
+
+### redirect the output of the ls command to a file and append to the file
+ls -l >> output.txt 2>&1
+```
+
+### Understanding the Pipe
+```bash
+### pipe the output of the ls command to the grep command
+ls -l | grep "file.txt"
+
+### pipe the output of the ls command to the grep command and display the line number
+ls -l | grep -n "file.txt"
+
+cat file.txt | wc -l # count the number of lines in the file
+```
+
+### Filtering with Grep
+```bash
+### grep the word "file" in the file.txt file
+grep "file" file.txt
+
+### grep the word "file" in the file.txt file and display the line number
+grep -n "file" file.txt
+```
+
+### Digging into Regular Expressions
+```bash
+### ^ matches the beginning of a line
+### $ matches the end of a line
+### . matches any single character
+### * matches zero or more of the preceding character
+### + matches one or more of the preceding character
+### ? matches zero or one of the preceding character
+### [a-z] matches any single character in the range a-z
+### [^a-z] matches any single character not in the range a-z
+
+### grep with regular expressions
+ls -a | grep ".py$" # grep the files that end with .py
+ls -a | grep "^.py" # grep the files that start with .py
+grep "^ch" file.txt # grep the lines that start with ch
+grep "^c.t$" file.txt # grep the lines that start with c and end with t but only if the line is exactly c.t
+grep "^c*t$" file.txt # grep the lines that start with c and end with t and have any number of characters in between
+grep "^[bc].*t$" file.txt # grep the lines that start with b or c and have any number of characters in between and end with t
+```
+
+### Head and Tail
+```bash
+### head
+head -n 5 file.txt # display the first 5 lines of the file
+
+### tail
+tail -n 5 file.txt # display the last 5 lines of the file
+tail -f file.txt # display the last 5 lines of the file and follow the file
+```
+
+### Creating Hard Links and Soft Links
+```bash
+### hard link is a physical link to the file
+ln file.txt file_link.txt # create a hard link to the file
+
+### soft link is a symbolic link to the file
+ln -s file.txt file_link.txt # create a soft link to the file
+```
+
+## Create & Transform Text Files
+
+### Text Editing with Nano
+```bash
+nano file.txt # edit the file
+
+### save and exit
+ctrl + x
+
+ctrl + o # save the file
+```
+
+### Understanding Vim Basics
+```bash
+vim file.txt # edit the file
+
+### open vim with line number
+vim +5 file.txt # open the file and go to line 5
+
+### exit without saving
+:q!
+
+### save and exit
+:wq
+
+### insert mode
+i # insert mode
+
+### command mode
+: # command mode
+
+### search
+/ # search
+
+### search and replace
+:%s/old/new/g # replace all instances of old with new
+
+:%! sort # sort the file
+
+### navigation
+h # move left
+j # move down
+k # move up
+l # move right
+
+2h # move 2 characters left
+37j # move 37 lines down
+```
+
+### Digging Deeper with Vim
+```bash
+### vim with line number
+vim +5 file.txt # open the file and go to line 5
+
+### vim with line number and column number
+vim +5:10 file.txt # open the file and go to line 5 and column 10
+
+dd # delete the current line
+
+5dd # delete the next 5 lines
+
+yy # copy the current line
+p # paste the copied line
+u # undo the last action
+
+d2j # delete the current line and move the cursor to the next line
+dip # quickly delete the current paragraph
+yip # quickly copy the current paragraph
+```
+
+### Manipulating Files with Awk
+```bash
+awk '{print $1}' file.txt # print the first field
+
+awk '{print $1, $2}' file.txt # print the first and second fields
+
+awk '{print "Hello, " $1}' file.txt # print "Hello, " and the first field
+
+awk -F: '{print $NF}' file.txt # print the last field separated by a colon
+```
+
+### Manipulating Files with Sed
+```bash
+sed 's/old/new/' file.txt # replace old with new
+
+sed 's/old/new/g' file.txt # replace all instances of old with new
+```