Some commands in Unix

Head and Tail

it allows you to clip the data by line numbers (-n) or by bytes. The following example is to print the 1st 1K bytes of the last 2000000K bytes of a file.

tail --bytes=2000000K test.dbf | head --bytes=1k

Zip and unzip a folder

gzip can only zip a single file. If you want to zip a folder, need to use “tar”: example:

$ tar -zcvf tian.tar.gz /home/tian

to untar:

$ tar -zxvf tian.tar.gz

if it’s .tar instead of .tar.gz, then remove the -z

$ tar -xvf tian.tar

Change permission

$ chmod a=rwx ./*        #changes all to read, write, and executable
$ chmod -R go-w TMPAV7/    #removes the write permission from group or other for all files in TMPAV7 directory

Find string in a directory

$ grep -r "boo" /path/to/file  #find all file with "boo" 

Hotkey

ctrl+alt+F1 to exit x window startx to open x window ctrl+alt+* to kill the front process

File download

using wget to download files from http sites

$ #download a single file
$ wget http://hydrology.princeton.edu/data/pgf/0.5deg/daily/prcp_daily_1948-1948.nc
$ #download a directory without including the index.html files
$ wget -r --no-parent --reject "index.html*" ftp://gmaoftp.gsfc.nasa.gov/pub/data/sarith/TianZhou/

using ncftpget to download files from ftp sites

$ ncftpget ftp://ftp.hydro.washington.edu/pub/tizhou/xxx.bin

Count number of files in a dir

$ ls -l | wc -l

Split an ascii file into several parts by line

$ split -l 2000 inflie.asc

Cut columns from a file with fixed delimiter (e.g. soil parameter)

-d: delimiter, default is tab -f: cut by field; -c: cut by characters; -b: cut by bytes

cut -d " " -f 1-53 soil.current &gt; newsoil   #cut soil.current 1-53 columns by space

See the first and last 10 lines of a text file

$ (head;echo;tail) < file.txt

AWK

file I/O output 1st and 3rd columns

$ awk '{print $1, $3}' PNW.KW.flow.151dams > junk.txt

it can also read some columns from one file and write some of the columns to another file -F is to define the delimiter in the read in file.

$ awk -F',' '{printf("%.1f,%.1f,%.4f\n", $4, $5, $3)}' in.csv > out.txt

Shortcuts and tricks

Change directory to your previous location $ cd -
Last command argument:!$ example:
```
$ mkdir temp
$ cd !$
```

Last command argument: !! example:

$ ping google.c
$ ping !!om     # this will give you "ping google.com"

Combine multiple lines to one line

$ less test.txt | - - -&gt; newtest.txt   
# every three lines in old file goes to one line in new file