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Bash Command Basics - initially created for ISM 4323 at USF
Bash
File system Root |
/ - top of file hierarchy |
Path |
either absolute or relative |
pwd |
present working directory |
cd |
change directory |
~ |
indicates home directory |
.. |
moving up to folder above current |
. |
current folder |
| |
ls |
lists all |
ls -F |
lists only folders |
ls -l |
show details |
ls -a |
show hidden files |
ls -al |
show hidden files + details |
mkdir |
creates folders |
rmdir |
removes folders |
cp |
copy |
mv |
move; can also be used to rename a file |
rm |
remove command |
-i |
adds interactivity; warning if will delete an existing file |
UNIX file systems are CASE SENSITIVE
Folders are directories
Copying and Moving Files
General syntax - <command> <source> <target>
Examples - cp hello.txt hello_world.txt
Notes on cp & mv
'cp' is only top level files, does not get what is in folders only folders on top
'mv' is always recursive
'cp -r' - copies a directory including all its content
Invasive Commands
'cp', 'mv', and 'rm' - no recovery possible
File Permissions
ls -al |
10 charactesr; (1)file type + (9)file permissions |
rwx |
read, write, execute |
owner, group, world |
order which permissions are displayed |
r |
4 - indicates read permission |
w |
2 - indicates write permission |
x |
1 - indicates execute permission |
r-x |
read and execute (5) |
755 |
rwe-er-er |
Conditionals
IF/THEN |
if [ <condition> ] then <commands> fi |
fi |
terminates IF/THEN |
if_[_<equation>_] |
-eq |
is equal to (integer) |
-ne |
is not equal to (integer) |
-gt |
greater than (integer) |
-lt |
less than (integer) |
-ge |
greater than or equal to (integer) |
-le |
less than or equal to (integer) |
= |
is equal to (string) |
!= |
is not equal to (string) |
ELIF |
alternative to nested-if statements |
read |
reads user input |
bash <directory> <variables> |
remember to put variables at end if variables are needed for command |
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Shell Scripting
grep <word> |
print lines matching a pattern |
redirect operator |
(>) send output to file instead of displaying on screen |
append operator |
(>>) appends data instead of displaying on screen |
cut -d" " |
cut empty columns |
cut -d, -f1,2,4 |
cuts out only columns 1,2,4 |
sort |
sorts alphabetically |
sort -n |
sorts numerically |
uniq |
removes duplicate lines from a text file; MUST BE SORTED FORT |
tr "abc" "xyz" |
subsitute <v1> to <v2> |
tr "[:lower:]""[:upper:]" |
specify all lowercase letters to turn uppercase |
new variable |
supply variable name and its value; no spaces inbetween |
variable1=2 |
valid; no spaces between equals |
$((<equation>)) |
arithmetic expansion |
echo $<variable> |
prints <variable value> |
" " |
does not affect use |
' ' |
used literally, does not call variables |
$USER |
lists current user |
$PWD |
prints present working directory |
$HOME |
home directory of current user |
$RANDOM |
o and 32767 |
sleep # |
sleeps for # seconds |
find
find |
search for files |
find [where to start searching from][expression to fine][-options][what to find] |
takes 2 arguements; where to search & what to find; wildcards can be used |
find /home -user alice -empty |
finds files in the home folder from alice which are empty |
Wildcards & Examples
Wildcards |
? |
matches a single character |
* |
matches any zero or more characters |
[x..y] |
matches a range of letters or numbers |
Examples |
ls |
lists all files + extensions |
ls *.doc |
lists only files with .doc extensions |
re - r <target> |
removes folders with content; be very careful |
While Loops
while |
run until a specific conditions is met |
CTRL+C |
to close script |
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vim - file editor
vim "filename" |
starts up in command mode |
i |
insert mode - start typing |
:w |
write |
:q |
quit vim type |
:wp |
save and quit |
:q! |
quit w/o saving |
/word |
search towards end of file for first occurance of word |
?word |
search towards beginning of the file for the word |
n |
search for next occurance |
N |
search for previous occurance |
less |
view file contents one screen at a time |
head |
top of file to see if it is the one you need |
head -3 |
show the first three results |
tail |
bottom of file to see new log entries |
-n |
default output of ten line |
-n# |
changes number of lines outputed |
-n & -n# |
to be used with head or tail |
YUM |
YUM |
yellowdog updater modifier - package modifier |
chmod
chmod |
updates permissions on files and folders |
su |
grants super user privileges |
ls -laF |
lists all folders + access |
chmod 775 engineering |
changes permissions for the engineering folders |
chown |
change ownership |
chgrp |
change group |
chown dave README |
changes owner of README to dave |
chgrp sales_grp README |
changes the group that can access README to sales_grp |
Encryption
aescrypt |
secret key encryption |
-e |
encrypt the file |
-d |
decrypt the file |
-p <password> |
password to use; if omitted, the command will prompt the user |
-o <filename> |
output file |
md5sum |
easy way to generate a checksum |
#! /bin/bash |
turns list of commands into one command // no need for bash ... |
For Loops
for var in <item/directory> do <commands> done |
how to format for loops |
Sequences |
{#..#} |
#..# |
first # starting value .. second# ending value |
#1..#2..#3 |
#3 is increment between each number series |
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