I realise this thread is over a month old, but I'll add my input even if it's no longer useful to the original poster, but just for others browsing. I realise the following code is far from elegant (ugly would be a good word), but it "works" (namely, it allows you to read full lines including nulls into a string for processing, one line at a time, without losing the nulls, using only Bash builtins).
Bash treats strings the same as C does (null-terminated), so it is obviously impossible to read in strings containing true nulls. The following code only breaks from the loop when the "read" command returns null (\0) twice in a row without other intervening text. It optionally adds an escaped null back into the string with each non-terminal read.
Generally it is far less painful to use something like Perl for this, but if you really are stuck in Bash and need a solution without external tools, maybe this will help.
Quote:
(And, it seems to me, there is some glitch in bash-2.05 in processing pipe by while (something about that I've experiensed about half year ago.) Seems something with asigning variables...
So, another point why I do not like that solution by 'tr..'
When bash reads from a pipe it spawns a subshell, so any variables you assign within the subshell will disappear after the command/loop which reads from the pipe finishes. It's not a "glitch", it's a feature. Using shell redirection avoids this. For example:
STEP 1
# Set variable
FILE=/tmp/mainfile
SEARCHFILE =/tmp/searchfile
# THIS IS THE MAIN FILE.
cat /tmp/mainfile
Interface Ethernet0/0 "outside", is up, line protocol is up
Hardware is i82546GB rev03, BW 100 Mbps
Full-Duplex(Full-duplex), 100 Mbps(100 Mbps)
MAC address... (6 Replies)
Hi ,
I am trying to write an shell, which reads a text file (from a location) having a list of numbers of strictly 5 digits only ex: 33144
Now my script will check :
1) that each entry is only 5 digits & numeric only, no alphabets, & its not empty.
2)then it executes a shell script called... (8 Replies)
Hi All,
I'm trying to figure out which are the trusted-ips and which are not using a script file.. I have a file named 'ip-list.txt' which contains some ip addresses and another file named 'trusted-ip-list.txt' which also contains some ip addresses. I want to read a line from... (4 Replies)
hello all
I'm writing a bash script and I need to read data from a file line by line
The number of words of each line is not known and I want to check if anywhere
in the line exists the substring www..That substring is a string by itself
or a substring of other strings.So what I tried so far... (4 Replies)
Hello,
I need a program that read a file line by line and prints out lines 1, 2 & 3 after an empty line... An example of entries in the file would be:
SRVXPAPI001 ERRO JUN24 07:28:34 1775
REASON= 0000, PROCID= #E506 #1065: TPCIPPR, INDEX= 003F
... (8 Replies)
Hi All,
Am trying to write wrapper shell/bash script on a utility tool for which i need to pass 2 files as arugment to execute utility tool.
Wraper script am trying is to do with above metion 2 files.
utility tool accepts :
a. userinfo file : which contains username
b. item file : which... (2 Replies)
Hi all,
I have a log file say Test.log that gets updated continuously and it has data in pipe separated format. A sample log file would look like:
<date1>|<data1>|<url1>|<result1>
<date2>|<data2>|<url2>|<result2>
<date3>|<data3>|<url3>|<result3>
<date4>|<data4>|<url4>|<result4>
What I... (3 Replies)
Heyas
I'm trying to read/display a file its content and put borders around it (tui-cat / tui-cat -t(ypwriter).
The typewriter-part is a 'bonus' but still has its own flaws, but thats for later.
So in some way, i'm trying to rewrite cat using bash and other commands.
But sadly it fails on... (2 Replies)
Hello,
I'm works on Ubuntu server
My goal : I would like to read file line per line, but i want to started at the end of file.
Currently, I use instructions :
while read line;
do
COMMAND
done < /var/log/apache2/access.log
But, the first line, i don't want this. The file is long... (5 Replies)
I have a file
file_name_O.txt
The file can have different number of other files names or nothing
I will check
cnt=`wc -l file_name_0.txt`
if ;then
exit 1
fi
Now I have to start checking file names, i.e. read txt file line by line. If amount of ,lines equal 1, I can... (4 Replies)
Discussion started by: digioleg54
4 Replies
LEARN ABOUT SUNOS
read
read(1) User Commands read(1)NAME
read - read a line from standard input
SYNOPSIS
/usr/bin/read [-r] var...
sh
read name...
csh
set variable = $<
ksh
read [ -prsu [n]] [ name ? prompt] [name...]
DESCRIPTION
/usr/bin/read
The read utility will read a single line from standard input.
By default, unless the -r option is specified, backslash () acts as an escape character. If standard input is a terminal device and the
invoking shell is interactive, read will prompt for a continuation line when:
o The shell reads an input line ending with a backslash, unless the -r option is specified.
o A here-document is not terminated after a NEWLINE character is entered.
The line will be split into fields as in the shell. The first field will be assigned to the first variable var, the second field to the
second variable var, and so forth. If there are fewer var operands specified than there are fields, the leftover fields and their interven-
ing separators will be assigned to the last var. If there are fewer fields than vars, the remaining vars will be set to empty strings.
The setting of variables specified by the var operands will affect the current shell execution environment. If it is called in a subshell
or separate utility execution environment, such as one of the following:
(read foo)
nohup read ...
find . -exec read ... ;
it will not affect the shell variables in the caller's environment.
The standard input must be a text file.
sh
One line is read from the standard input and, using the internal field separator, IFS (normally space or tab), to delimit word boundaries,
the first word is assigned to the first name, the second word to the second name, and so on, with leftover words assigned to the last name.
Lines can be continued using
ewline. Characters other than NEWLINE can be quoted by preceding them with a backslash. These backslashes
are removed before words are assigned to names, and no interpretation is done on the character that follows the backslash. The return code
is 0, unless an end-of-file is encountered.
csh
The notation:
set variable = $<
loads one line of standard input as the value for variable. (See csh(1)).
ksh
The shell input mechanism. One line is read and is broken up into fields using the characters in IFS as separators. The escape character,
(), is used to remove any special meaning for the next character and for line continuation. In raw mode, -r, the character is not
treated specially. The first field is assigned to the first name, the second field to the second name, and so on, with leftover fields
assigned to the last name. The -p option causes the input line to be taken from the input pipe of a process spawned by the shell using |&.
If the -s flag is present, the input will be saved as a command in the history file. The flag -u can be used to specify a one digit file
descriptor unit n to read from. The file descriptor can be opened with the exec special command. The default value of n is 0. If name is
omitted, REPLY is used as the default name. The exit status is 0 unless the input file is not open for reading or an end-of-file is encoun-
tered. An end-of-file with the -p option causes cleanup for this process so that another can be spawned. If the first argument contains a
?, the remainder of this word is used as a prompt on standard error when the shell is interactive. The exit status is 0 unless an end-of-
file is encountered.
OPTIONS
The following option is supported:
-r Does not treat a backslash character in any special way. Considers each backslash to be part of the input line.
OPERANDS
The following operand is supported:
var The name of an existing or non-existing shell variable.
EXAMPLES
Example 1: An example of the read command
The following example for /usr/bin/read prints a file with the first field of each line moved to the end of the line:
example% while read -r xx yy
do
printf "%s %s
" "$yy" "$xx"
done < input_file
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of read: LANG, LC_ALL, LC_CTYPE, LC_MES-
SAGES, and NLSPATH.
IFS Determines the internal field separators used to delimit fields.
PS2 Provides the prompt string that an interactive shell will write to standard error when a line ending with a backslash is read and
the -r option was not specified, or if a here-document is not terminated after a newline character is entered.
EXIT STATUS
The following exit values are returned:
0 Successful completion.
>0 End-of-file was detected or an error occurred.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), ksh(1), line(1), set(1), sh(1), attributes(5), environ(5), standards(5)SunOS 5.10 28 Mar 1995 read(1)