Sponsored Content
Top Forums Shell Programming and Scripting How to understand special character for line reading in bash shell? Post 303039063 by RudiC on Saturday 21st of September 2019 02:24:23 PM
Old 09-21-2019
Not sure I'm an expert nor a guru, but this is what I'd do: refer to the respective man pages.
man bash:
Quote:
Parameter Expansion

${parameter#word}
${parameter##word}

Remove matching prefix pattern.


${parameter%word}
${parameter%%word}

Remove matching suffix pattern.



CONDITIONAL EXPRESSIONS.



An additional binary operator, =~, is available, with the same precedence as == and !=. When it is used, the string to the right of the operator is considered a POSIX extended regular expression and matched accordingly (as in regex(3))
Of course you need to learn the difference between shell's pattern matching and regex matching.

man regex:
Quote:
An atom is a regular expression ... '^' (matching the null string at the beginning of a line)

A bracket expression is a list of characters enclosed in "[]". It normally matches any single character from the list (but see below). If the list begins with '^', it matches any single character (but see below) not from the rest of the list.
Admittedly the ambiguous use of the caret is something you need to accustom to.
These 2 Users Gave Thanks to RudiC For This Post:
 

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

[OpenServer 5]Line Printing and special character (é @)

Hello, On Sco OpenServer 5, i want to print using the lpr command, no CUPS installed. I print on an HP LaserJet 4050 on LAN (IP 192.168.x.x) the printer is installed by HP Network Printer service. it works fine, but Specials characters, like é, @ or ° print bad characters. Is there... (5 Replies)
Discussion started by: tankd
5 Replies

2. Shell Programming and Scripting

bash shell: 'exec', 'eval', 'source' - looking for help to understand

Hi, experts. Whould anybody clear explay me difference and usage of these 3 commands (particulary in bash) : exec eval source I've tryed to read the manual pages but did not get much. Also could not get something useful from Google search - just so much and so not exactly, that is... (3 Replies)
Discussion started by: alex_5161
3 Replies

3. Shell Programming and Scripting

Adding a special character at the end of the line

I used following to add * at the end of the line in file1. It adds * at the end but has a space before it for some lines but some other lines it adds exactly after the last character. How do I take out the space ? sed 's/$/*/' file1 > file2 example: contents of file1 : ... (2 Replies)
Discussion started by: pitagi
2 Replies

4. Shell Programming and Scripting

How to insert a character in line in Special condition?

Hi, I have a log file generated by a tool which has the following look : /tmp/releases/directory/datefilename1_release_date.zip /tmp/releases/directory/datefilename2_release_date.zip /tmp/releases/directory/datefilename3_release_date.zip... (8 Replies)
Discussion started by: bhaskar_m
8 Replies

5. Shell Programming and Scripting

I need to understand the differences between the bash shell and the Bourne shell

I do not claim to be an expert, but I have done things with scripts that whole teams of folks have said can not be done. Of course they should have said we do not have the intestinal fortitude to git-r-done. I have been using UNIX actually HPUX since 1992. Unfortunately my old computer died and... (7 Replies)
Discussion started by: awk_sed_hello
7 Replies

6. Shell Programming and Scripting

Printing special character in bash

I am using this character as a delimiter 'þ' Currently, I set it straight: DELIMITER='þ' However, while copying the file, this character often gets mangled. Is there a bash way (perhaps using tr or printf) of generating this character. It corresponds to "chr(0xfe)" if using perl. (I've... (6 Replies)
Discussion started by: sentinel
6 Replies

7. Shell Programming and Scripting

parse special character in the line

Hi all, I have a file with some module names as below. Font::AFM Data::Grove ---> libxml-perl Net::LDAP ---> perl-ldap DBI XML .... ... .... and so on ... The file has some lines with the character " -->" . Now how can I cut only the last column of the line wherever "-->" is... (4 Replies)
Discussion started by: vijaya2006
4 Replies

8. UNIX for Dummies Questions & Answers

Reading character by character - BASH

Hello every one and thanks in advance for the time you will take to think about my problem. I would like to know if it's possible (in BASH) to read a text file character after character. Exactly this is what I would like to do : Txt file : ATGCAGTTCATTGCCAAA...... (~2.5 millions... (3 Replies)
Discussion started by: sluvah
3 Replies

9. Shell Programming and Scripting

Shell script question in special character

when I execute the unix commands its works normally in the 1st part. When I the tried the same in shell scripting the directory is not displayed in 2nd part example. please let me know what needs to be done. Unix : client=~zsvdbs echo $client /shome/zsvhome/zsvdbs Using... (3 Replies)
Discussion started by: keerthi2016
3 Replies

10. UNIX for Beginners Questions & Answers

Escape bash-special character in a bash string

Hi, I am new in bash scripting. In my work, I provide support to several users and when I connect to their computers I use the same admin and password, so I am trying to create a script that will only ask me for the IP address and then connect to the computer without having me to type the user... (5 Replies)
Discussion started by: arcoa05
5 Replies
read(1) 						      General Commands Manual							   read(1)

NAME
read - read a line from standard input SYNOPSIS
var ... DESCRIPTION
reads a single line from standard input. The line is split into fields as when processed by the shell (refer to shells in the first field is assigned to the first variable var, the second field to the second variable var, and so forth. If there are more fields than there are specified var operands, the remaining fields and their intervening separators are assigned to the last var. If there are more vars than fields, the remaining vars are set to empty strings. The setting of variables specified by the var operands affect the current shell execution environment. Standard input to can be redirected from a text file. Since affects the current shell execution environment, it is usually provided as a normal shell special (built-in) command. Thus, if it is called in a subshell or separate utility execution environment similar to the following, it does not affect the shell variables in the caller's environment: Options recognizes the following options: Do not treat a backslash character in any special way. Consider each backslash to be part of the input line. Opperands recognizes the following operands: var The name of an existing or nonexisting shell variable. EXTERNAL INFLUENCES
Environment Variables determines the internal field separators used to delimit fields. RETURN VALUE
exits with one of the following values: 0 Successful completion. >0 End-of-file was detected or an error occurred. EXAMPLES
Print a file with the first field of each line moved to the end of the line. while read -r xx yy do printf "%s %s " "$yy" "$xx" done < input_file SEE ALSO
csh(1), ksh(1), sh(1), sh-posix(1). STANDARDS CONFORMANCE
read(1)
All times are GMT -4. The time now is 03:08 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy