Bash Shell: Check File Exists or Not
H ow do I test existence of a text file in bash running under Unix like operating systems?
You need to use the test command to check file types and compare values. The same command can be used to see if a file exist of not. The syntax is as follows:
The following command will tell if a text file called /etc/hosts exists or not using bash conditional execution :
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The same code can be converted to use with if..else..fi which allows to make choice based on the success or failure of a test command:
File test operators
The following operators returns true if file exists:
(Fig.01: File test operators taken from bash man page)
The syntax is same (see File operators (attributes) comparisons for more info):
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Comments on this entry are closed.
Thank you for the trick!
thanks much for that useful information
i made a linux script which receives as first argument a path to a directory. I don’t know the path. And i want to check if “file.txt” exists at that certain path . For example :
if [ -e $1/file.txt ];then echo HAHA fi
if you use -f with *.sock files it always says “the file does not exist”. when I use -e it worked 🙂
What if I want to test for the existence of any files with a particular filename extension? Is there a simple way to do that? I’ve trying to use the return status of the ls command but I seem to be getting the syntax a bit wrong.
You can use wildcard. Ex:
[ -e *”.extension” ]
(don’t forget to have a space character before the operator and before the closing branch, it took hours of my time to recognize this 😐 )
Can I mix the operator?
like:
if [-xw filename]
(Checking the existence of the file that executable and writable)
i want to write script to copy a some of the files inside directory to specified location(for example i have one directory, this containes 1000 image file. then i need pick only 100 image file from 1000 image file. also i have a list of images which i need to copy (i made one file).
can anyone help on this(please forword to my mail)
in my script I have[ $FILE ! = “”] ..what does it mean…
FILE has lot ma y rows extracted file names from database.
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Linux Shell Commands
The Shell is the command interpreter on Linux systems. This document intoduces some of the basic features of the Shell and lists many of the commands or programs available on the Linux computers in Cardiff School of Computer Science & Informatics.
The Shell
The Linux command interpreter or shell is the program users interact with in a terminal emulation window. The terminal emulation window can be one in the workstation’s Graphical User Interface mate-terminal on Linux. Alternatively, it can be an application such as SSH secure shell client or PuTTY on a Windows PC that’s logged into Linux over the network.
The shell used in the School of Computer Science & Informatics is bash Bourne Again Shell. There are other shells available such as the Bourne Shell, the C-Shell and the TC-Shell, and you can choose to use a different shell if you prefer. They all have similar characteristics but each has its own particular features. This document assumes you are using bash .
Bash has the following features:
A command prompt which may be configured by the user. The default prompt is a dollar symbol preceded by «bash» and the bash program’s version number.
/bin containing the following.
/bin/countc
bash-2.05$ countc
45
516 ls -lrt
517 ps -ef
518 pdflatex myfile.tex
See the manual page on bash for more details (type man bash ).
Bash has an additional mechanism which allows you to recall and edit previous commands using the keyboard up-arrow key. If you press up-arrow, the last command re-appears on the terminal. Press up-arrow again to get earlier commands. To rerun the command, press RETURN . To amend the command before rerunning it, use the delete key to remove characters from the end or use the back-arrow key to reposition the cursor to delete or insert characters within the command.
Shell Commands
Here is a summary of some of the commands available. For more details refer to the manual page of each command. You can see these on-line by using the man command. Just type man followed by the name of the command you want to see.
Logging out
| Command | Description |
| logout | log out of a Linux terminal |
Note, on a Linux workstation you will need to exit the Desktop Environment instead.
Files and Directories
These commands allow you to create directories and handle files.
| Command | Description |
|---|---|
| cat | concatenate and print data |
| lpr | spool file for line printing |
| cd | change current directory |
| lprm, cancel | remove jobs from line printer queue |
| chgrp | change file group |
| ls | list and generate statistics for files |
| chmod | change file mode |
| mkdir | make a new directory |
| cp | copy file data |
| more, page | display file data at your terminal |
| Command | Description |
|---|---|
| file | determine file type |
| mv | move or rename files |
| find | find files |
| pwd | print working directory |
| grep | search file for regular expression |
| rm, rmdir | remove (unlink) files or directories |
| head | give first few lines |
| tail | print last lines from file |
| just | text justification program |
| touch | update access and modification times of a file |
| lpq | spool queue examination program |
File Editors
Editors are used to create and amend files.
| Command | Description |
|---|---|
| emacs | GNU project Emacs |
| xemacs | emacs with mouse action |
| ex, edit | line editor |
| Command | Description |
|---|---|
| pico | easy text editor for vdus |
| pluma | Mate GUI text editor |
| gedit | GNOME text editor |
| vi, vim | standard text editor |
Vi , pico and emacs are screen-based editors which run on a vdu or in a workstations terminal emulation window; pluma , gedit and xemacs are graphical user interface (GUI) based editors with cut and paste and mouse-controlled cursor positioning.
Manipulating data
The contents of files can be compared and altered with the following commands.
| Command | Description |
| awk | pattern scanning and processing language |
| perl | data manipulation language |
| cmp | compare the contents of two files |
| paste | merge file data |
| comm | compare sorted data |
| sed | stream text editor |
| cut | cut out selected fields of each line of a file |
| sort | sort file data |
| diff | differential file comparator |
| Command | Description | split | split file into smaller files |
|---|---|
| expand, unexpand | expand tabs to spaces, and vice versa |
| tr | translate characters |
| gawk | pattern scanning and processing language |
| uniq | report repeated lines in a file |
| join | join files on some common field |
| look | find lines in sorted data |
| wc | count words, lines, and characters |
Compressed files
Files may be compressed to save space. Compressed files can be created and examined.
| Command | Description |
|---|---|
| gzip | compress files |
| zmore | file perusal filter for crt viewing of compressed text |
| uncompress | uncompress files |
| Command | Description |
|---|---|
| zcat | cat a compressed file |
| gunzip | uncompress gzipped files |
| zcmp, zdiff | compare compressed files |
Information
Manuals and documentation are available on-line. Go to our web site www.cs.cf.ac.uk/systems for web-based documentation. The following Shell commands give information.
| Command | Description |
| apropos | locate commands by keyword lookup |
| man | displays manual pages online |
| Command | Description |
|---|---|
| info | displays command information pages online |
| yelp | GNOME help viewer |
Status
These commands list or alter information about the system.
| Command | Description |
| ps | print process status statistics |
| date | print the date |
| quota -v | display disk usage and limits |
| reset | reset terminal mode |
| du | print amount of disk usage |
| script | keep script of terminal session |
| stty | set terminal options |
| groups | show group memberships |
| time | time a command |
| homequota | show quota and file usage |
| iostat | report I/O statistics |
| tty | print current terminal name |
| Command | Description |
|---|---|
| kill | send a signal to a process |
| uptime | display system status |
| last | show last logins of users |
| users | print names of logged in users |
| lun | list user names or login ID |
| vmstat | report virtual memory statistics |
| netstat | show network status |
| w | show what logged in users are doing |
| who | list logged in users |
| printenv | display value of a shell variable |
Printing
Files can be printed using shell commands, using the GUI print manager, or direct from some applications.
You must specify a printer by name. Printers are called
| Printer Name | Location |
|---|---|
| tl1_lw | Teaching Lab 1 (C/2.04) laser printer |
| tl3_lw | Teaching Lab 3 (C/2.08) laser printer |
| Printer Name | Location |
|---|---|
| tl2_lw | Teaching Lab 2 (C/2.05) laser printer |
| tl4_lw | Teaching Lab 4 (C/2.10) laser printer |
Most commands which can be used to print files, expect the printer name to be given following a -P argument.
Files may be sent to the printers as simple text files or they may be processed in various ways for the laser printers.
| Command | Description |
|---|---|
| lpr -P printer | send a file to a printer |
| dvips -P printer | postprocess TeX file into Postscript and print on laser printer |
| a2ps -P printer | format text file in PostScript and print on laser printer |
Messages between Users
The Linux systems support on-screen messages to other users and world-wide electronic mail.
| Command | Description |
|---|---|
| write | send a message to another local user |
| wall | send a message to all local users |
| Command | Description |
|---|---|
| pine | vdu-based mail utility |
| simple send or read mail program | |
| thunderbird | GUI mail handling tool on Linux |
Networking
The School of Computer Science & Informatics is connected to the JANET Internet Protocol Service (JIPS), the UK Universities’ network.
These commands are used to send and receive files from Campus Linux hosts and from other hosts on JIPS and the Internet, that permit such connections, around the world.
| Command | Description |
|---|---|
| ftp | file transfer program |
| tftp | trivial file transfer program |
| sftp | secure shell file transfer program |
| rcp | remote file copy |
| scp | secure shell remote file copy |
| wget | non-interactive network downloader |
| Command | Description |
|---|---|
| telnet | make terminal connection to another host |
| ssh | secure shell terminal or command connection |
| rlogin | remote login to a Linux host |
| rsh | remote shell |
| curl | transfer data from a url |
| firefox | web browser |
| google-chrome | web browser |
These commands work only where the remote host permits such connections.
Programming
The following programming tools and languages are available.
General
| Command | Description |
|---|---|
| make | maintain groups of programs |
| size | print program’s sizes |
| Command | Description |
|---|---|
| nm | print program’s name list |
| strip | remove symbol table and relocation bits |
| Command | Description |
|---|---|
| cb | C program beautifier |
| gcc | GNU ANSI C Compiler |
| Command | Description |
|---|---|
| ctrace | C program debugger |
| indent | indent and format C program source |
| cxref | generate C program cross reference |
| Command | Description |
|---|---|
| g++ | GNU C++ Compiler |
| Command | Description |
|---|---|
| appletviewer | JAVA applet viewer |
| javac | JAVA compiler |
| eclipse | Java integrated development environment on Linux |
FORTRAN
| Command | Description |
| f95 | GNU Fortran 95 compiler |
Other Languages
(Not available on all systems).
| Command | Description |
| bc | interactive arithmetic language processor |
| matlab | maths package |
| gcl | GNU Common Lisp |
| perl | general purpose language |
| Command | Description |
|---|---|
| python | object-oriented programming language |
| squeak | smalltalk |
| php | web page embedded language |
| mathematica | symbolic maths package |
| asp | web page embedded language |
Text Processing
TeX is a typesetting language used extensively in Linux and other operating systems for producing high-quality printed documents. Another set of programs based on Troff is the standard Linux text formatting family used, for example to format manual pages.
General Commands
| Command | Description |
|---|---|
| fmt | simple text formatter |
| evince | GNOME PostScript previewer |
| Command | Description |
|---|---|
| acroread | PDF viewer |
| spell | check text for spelling error |
| aspell | interactive spelling checker |
Troff
| Command | Description |
|---|---|
| eqn | mathematical preprocessor for troff |
| tbl | prepare tables for nroff or troff |
| grap | pic preprocessor for drawing graphs |
| troff | text formatting and typesetting language |
| Command | Description |
|---|---|
| nroff | text formatting language |
| groff | GNU troff interface for laserprinting |
| pic | troff preprocessor for drawing pictures |
| Command | Description |
|---|---|
| tex | text formatting and typesetting |
| latex | latex formatter |
| Command | Description |
|---|---|
| pdflatex | latex formatter with PDF output |
| xdvi | dvi previewer |
| dvips | convert a DVI file to POSTSCRIPT |
Word Processing
LibreOffice is available on the School’s Linux systems and attempts compatibilty with Microsoft Office.
| Command | Description |
|---|---|
| libreoffice | start LibreOffice applications |
Database Management
MySQL and Oracle are available.
| Command | Description |
|---|---|
| sqlplus | run the Oracle SQL interpreter |
| mysql | run the mysql SQL interpreter |
| sqldeveloper | Oracle SQL Developer GUI interface |
| mysql-workbench | GUI interface for MySQL |
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