Related
I have the following inside of an environment variable (using Ubuntu):
variable="Hello: User"
If I do:
echo $variable
Hello: User
What I need to do is replace the : with - inside $variable.
echo $(echo $variable | sed '')
But I don't know how to use sed with a variable like this one.
My expected output from this command would be:
"Hello - User"
Use Bash string manipulation:
echo "${variable/:/ -}"
It will replace the first : with space + -.
I'm writing a script for looping over a set of files in a directory searching for a string (stringA) in one file (srcFile), copying the line that follows it (stringToCopy), and pasting it on the line after another search string (stringB) in another file (outputFile). The copy/paste script that I have so far is as follows
stringA="This is string A"
stringB="This is string B"
srcFile=srcFile.txt
outpuFile=outputFile.txt
replacement="/$stringA/{getline; print}"
stringToCopy="$(awk "$replacement" $srcFile)"
sed -i "/$stringB/!b;n;c${stringToCopy}" $outputFile
The script works great, except when stringToCopy ends up containing curly braces. Example is
srcFile.txt:
This is string A
text to copy: {0}
outputFile.txt:
This is string B
line to be replaced
Once the script is done, I would expect outputFile.txt to be
This is string B
text to copy: {0}
But sed chokes with
sed: -e expression #1, char 106: unknown command: `m'
I've tried hardcoding the problematic string and trying different variations of escaping the curlies and quoting the string, but haven't found a winning combination and I'm at a loss for how to make it work.
EDIT
I had a derp moment and forgot that my stringA also has curly braces, that happened to cause my awk command to math multiple lines. This caused my stringToCopy to have newlines in it which is my real issue, not the curly braces. So the real question is, how to make awk treat curly braces as literal characters so that
srcFile.txt
This is string A: {0}
text to copy: {0}
This is string A:
Other junk
And stringA="This is string A: {0}"
Doesn't set stringToCopy to
text to copy: {0}
Other junk
A bit of a kludge in that we're going to add some extra coding specifically for braces ...
Current situation:
$ awk '/This is string A: {0}/{getline; print}' srcFile.txt
text to copy: {0} # this is the line we want
Other junk # we do not want this line
We can eliminate the second line by escaping the braces in the search pattern, eg:
$ awk '/This is string A: \{0\}/{getline; print}' srcFile.txt
text to copy: {0}
So, how to escape the braces? We can use some explicit parameter expansions to replace the braces with escaped braces in the $stringA variable, keeping in mind that we also need to escape the braces in the parameter expansion phase, too:
$ stringA="This is string A: {0}"
$ stringA="${stringA//\{/\\{}" # replace '{' with '\{'
$ stringA="${stringA//\}/\\}}" # replace '}' with '\}'
$ echo "${stringA}"
This is string A: \{0\}
We can then proceed with the rest of the code as is:
$ replacement="/$stringA/{getline; print}"
$ echo "${replacement}"
/This is string A: \{0\}/{getline; print}
$ stringToCopy="$(awk "$replacement" $srcFile)"
$ echo "${stringToCopy}"
text to copy: {0}
As for the final sed step I had to remove the ! to get it to work correctly:
$ sed -i "/$stringB/b;n;c${stringToCopy}" $outputFile
$ cat "${outputFile}"
This is string B
text to copy: {0}
NOTES:
if you preface your coding with set -xv you can see how variables are being interpreted at each step; use set +xv to turn off
obviously you'll probably run into issues if you do in fact have more than 1 matching row in $srcFile
if you find other characters that need to be escaped then you'll need to add additional parameter expansions for said characters
I needed to write a script to enter multi-line input to a program (psql).
After a bit of googling, I found the following syntax works:
cat << EOF | psql ---params
BEGIN;
`pg_dump ----something`
update table .... statement ...;
END;
EOF
This correctly constructs the multi-line string (from BEGIN; to END;, inclusive) and pipes it as an input to psql.
But I have no idea how/why it works, can some one please explain?
I'm referring mainly to cat << EOF, I know > outputs to a file, >> appends to a file, < reads input from file.
What does << exactly do?
And is there a man page for it?
The cat <<EOF syntax is very useful when working with multi-line text in Bash, eg. when assigning multi-line string to a shell variable, file or a pipe.
Examples of cat <<EOF syntax usage in Bash:
1. Assign multi-line string to a shell variable
$ sql=$(cat <<EOF
SELECT foo, bar FROM db
WHERE foo='baz'
EOF
)
The $sql variable now holds the new-line characters too. You can verify with echo -e "$sql".
2. Pass multi-line string to a file in Bash
$ cat <<EOF > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
EOF
The print.sh file now contains:
#!/bin/bash
echo $PWD
echo /home/user
3. Pass multi-line string to a pipe in Bash
$ cat <<EOF | grep 'b' | tee b.txt
foo
bar
baz
EOF
The b.txt file contains bar and baz lines. The same output is printed to stdout.
This is called heredoc format to provide a string into stdin. See https://en.wikipedia.org/wiki/Here_document#Unix_shells for more details.
From man bash:
Here Documents
This type of redirection instructs the shell to read input from
the current source until a line
containing only word (with no trailing
blanks) is seen.
All of the lines read up to that point are then used as the
standard input for a command.
The format of here-documents is:
<<[-]word
here-document
delimiter
No parameter expansion, command substitution, arithmetic expansion, or
pathname expansion is performed on
word. If any characters in word are
quoted, the
delimiter is the result of quote removal on word, and the lines
in the here-document are not expanded.
If word is unquoted, all lines of the
here-document are subjected to parameter expansion, command
substitution, and arithmetic
expansion. In the latter case, the
character sequence \<newline> is
ignored, and \ must be used to quote the characters \, $, and `.
If the redirection operator is <<-, then all leading tab characters
are stripped from input lines and the
line containing delimiter. This
allows here-documents within shell scripts to be indented in a natural fashion.
In your case, "EOF" is known as a "Here Tag". Basically <<Here tells the shell that you are going to enter a multiline string until the "tag" Here. You can name this tag as you want, it's often EOF or STOP.
Some rules about the Here tags:
The tag can be any string, uppercase or lowercase, though most people use uppercase by convention.
The tag will not be considered as a Here tag if there are other words in that line. In this case, it will merely be considered part of the string. The tag should be by itself on a separate line, to be considered a tag.
The tag should have no leading or trailing spaces in that line to be considered a tag. Otherwise it will be considered as part of the string.
example:
$ cat >> test <<HERE
> Hello world HERE <-- Not by itself on a separate line -> not considered end of string
> This is a test
> HERE <-- Leading space, so not considered end of string
> and a new line
> HERE <-- Now we have the end of the string
POSIX 7
kennytm quoted man bash, but most of that is also POSIX 7: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04 :
The redirection operators "<<" and "<<-" both allow redirection of lines contained in a shell input file, known as a "here-document", to the input of a command.
The here-document shall be treated as a single word that begins after the next <newline> and continues until there is a line containing only the delimiter and a <newline>, with no <blank> characters in between. Then the next here-document starts, if there is one. The format is as follows:
[n]<<word
here-document
delimiter
where the optional n represents the file descriptor number. If the number is omitted, the here-document refers to standard input (file descriptor 0).
If any character in word is quoted, the delimiter shall be formed by performing quote removal on word, and the here-document lines shall not be expanded. Otherwise, the delimiter shall be the word itself.
If no characters in word are quoted, all lines of the here-document shall be expanded for parameter expansion, command substitution, and arithmetic expansion. In this case, the <backslash> in the input behaves as the <backslash> inside double-quotes (see Double-Quotes). However, the double-quote character ( '"' ) shall not be treated specially within a here-document, except when the double-quote appears within "$()", "``", or "${}".
If the redirection symbol is "<<-", all leading <tab> characters shall be stripped from input lines and the line containing the trailing delimiter. If more than one "<<" or "<<-" operator is specified on a line, the here-document associated with the first operator shall be supplied first by the application and shall be read first by the shell.
When a here-document is read from a terminal device and the shell is interactive, it shall write the contents of the variable PS2, processed as described in Shell Variables, to standard error before reading each line of input until the delimiter has been recognized.
Examples
Some examples not yet given.
Quotes prevent parameter expansion
Without quotes:
a=0
cat <<EOF
$a
EOF
Output:
0
With quotes:
a=0
cat <<'EOF'
$a
EOF
or (ugly but valid):
a=0
cat <<E"O"F
$a
EOF
Outputs:
$a
Hyphen removes leading tabs
Without hyphen:
cat <<EOF
<tab>a
EOF
where <tab> is a literal tab, and can be inserted with Ctrl + V <tab>
Output:
<tab>a
With hyphen:
cat <<-EOF
<tab>a
<tab>EOF
Output:
a
This exists of course so that you can indent your cat like the surrounding code, which is easier to read and maintain. E.g.:
if true; then
cat <<-EOF
a
EOF
fi
Unfortunately, this does not work for space characters: POSIX favored tab indentation here. Yikes.
Using tee instead of cat
Not exactly as an answer to the original question, but I wanted to share this anyway: I had the need to create a config file in a directory that required root rights.
The following does not work for that case:
$ sudo cat <<EOF >/etc/somedir/foo.conf
# my config file
foo=bar
EOF
because the redirection is handled outside of the sudo context.
I ended up using this instead:
$ sudo tee <<EOF /etc/somedir/foo.conf >/dev/null
# my config file
foo=bar
EOF
<< EoF basically means:
<< - "read the multi-line input that begins from the next line onward, and treat it as if it's code in a separate file"
EoF - "stop reading immediately after the word EoF is found in the multi-line input"
As other answers have explained, the multi-line input is called a Here Document
A Here Document is often used to generate output to be passed to a subsequent process. For example cat << EoF can be used to generate a desired output, using a Here Document.
Here's an example of using a Here Document to create a text document on the fly:
cat << EoF > ./my-document.txt
Hello world
Have a nice day
EoF
A little extension to the above answers. The trailing > directs the input into the file, overwriting existing content. However, one particularly convenient use is the double arrow >> that appends, adding your new content to the end of the file, as in:
cat <<EOF >> /etc/fstab
data_server:/var/sharedServer/authority/cert /var/sharedFolder/sometin/authority/cert nfs
data_server:/var/sharedServer/cert /var/sharedFolder/sometin/vsdc/cert nfs
EOF
This extends your fstab without you having to worry about accidentally modifying any of its contents.
note to mention that cat << \EOT (see the backslash) will not expand any variables inside, while cat << EOT will do.
examples:
FOO="bar"
cat << \EOT > foobar.txt
echo "$FOO"
EOT
will output:
echo $FOO
while:
FOO="bar"
cat << EOT > foobar.txt
echo "$FOO"
EOT
will output:
echo "bar"
Example to create a json file:
cat << EoF > ./allaccess.json
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"s3:*"
],
"Resource": [
"arn:aws:s3:::*"
]
}
]
}
EoF
As a result:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"s3:*"
],
"Resource": [
"arn:aws:s3:::*"
]
}
]
}
Long story short, EOF marker(but a different literal can be used as well) is a heredoc format that allows you to provide your input as multiline.
A lot of confusion comes from how cat actually works it seems.
You can use cat with >> or > as follows:
$ cat >> temp.txt
line 1
line 2
While cat can be used this way when writing manually into console, it's not convenient if I want to provide the input in a more declarative way so that it can be reused by tools and also to keep indentations, whitespaces, etc.
Heredoc allows to define your entire input as if you are not working with stdin but typing in a separate text editor. This is what Wikipedia article means by:
it is a section of a source code file that is treated as if it were a
separate file.
This isn't necessarily an answer to the original question, but a sharing of some results from my own testing. This:
<<test > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
test
will produce the same file as:
cat <<test > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
test
So, I don't see the point of using the cat command.
Worth noting that here docs work in bash loops too.
This example shows how-to get the column list of table:
export postgres_db_name='my_db'
export table_name='my_table_name'
# start copy
while read -r c; do test -z "$c" || echo $table_name.$c , ; done < <(cat << EOF | psql -t -q -d $postgres_db_name -v table_name="${table_name:-}"
SELECT column_name
FROM information_schema.columns
WHERE 1=1
AND table_schema = 'public'
AND table_name =:'table_name' ;
EOF
)
# stop copy , now paste straight into the bash shell ...
output:
my_table_name.guid ,
my_table_name.id ,
my_table_name.level ,
my_table_name.seq ,
or even without the new line
while read -r c; do test -z "$c" || echo $table_name.$c , | perl -ne
's/\n//gm;print' ; done < <(cat << EOF | psql -t -q -d $postgres_db_name -v table_name="${table_name:-}"
SELECT column_name
FROM information_schema.columns
WHERE 1=1
AND table_schema = 'public'
AND table_name =:'table_name' ;
EOF
)
# output: daily_issues.guid ,daily_issues.id ,daily_issues.level ,daily_issues.seq ,daily_issues.prio ,daily_issues.weight ,daily_issues.status ,daily_issues.category ,daily_issues.name ,daily_issues.description ,daily_issues.type ,daily_issues.owner
I have a list of strings and I want to pass those strings as arguments in a single Windows command line call. For simple alphanumeric strings it suffices to just pass them verbatim:
> script.pl foo bar baz yes no
foo
bar
baz
yes
no
I understand that if an argument contains spaces or double-quotes, I need to backslash-escape the double-quotes and backslashes, and then double-quote the argument.
> script.pl foo bar baz "\"yes\"\\\"no\""
foo
bar
baz
"yes"\"no"
But when I try to pass an argument with literal percent signs, this happens:
> script.pl %PATH%
C:\Program
Files\PHP\;C:\spaceless\perl\bin\;C:\Program
Files\IBM\Java60\bin;
(...etc.)
Double quoting doesn't work:
> script.pl "%PATH%"
C:\Program Files\PHP\;C:\spaceless\perl\bin\;C:\Program Files\IBM\Java60\bin; (...etc.)
Nor does backslash-escaping (notice how the backslashes are present in the output):
> script.pl \%PATH\%
\%PATH\%
Also, the rules are inconsistent for backslash-escaping backslashes:
> script.pl "\\yes\\"
\\yes\
> script.pl "\yes\\"
\yes\
> script.pl "\yes\"
\yes"
Also, doubtless there are special characters in the Windows command line shell, much like there are in all shells. What, then, is the general procedure for safely escaping arbitrary command line arguments for use at the Windows command line?
The ideal answer will describe a function escape() which can be used in situations like the following (a Perl example):
$cmd = join " ", map { escape($_); } #args;
Here are some more example strings which should be safely escaped by this function (I know some of these look Unix-like, that's deliberate):
yes
no
child.exe
argument 1
Hello, world
Hello"world
\some\path with\spaces
C:\Program Files\
she said, "you had me at hello"
argument"2
\some\directory with\spaces\
"
\
\\
\\\
\\\\
\\\\\
"\
"\T
"\\T
!1
!A
"!\/'"
"Jeff's!"
$PATH
%PATH%
&
<>|&^
()%!^"<>&|
>\\.\nul
malicious argument"&whoami
*#$$A$##?-_
Here is an msdn blogpost showing how. It however assumes that every command line program internally uses CommandLineToArgvW to parse it's command line (not a shabby assumption, since it's part of the Shell32 library).
Original link (may not work): http://blogs.msdn.com/b/twistylittlepassagesallalike/archive/2011/04/23/everyone-quotes-arguments-the-wrong-way.aspx
Web archive link: https://web.archive.org/web/20190109172835/https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/
To escape a command line argument, use the following:
sub escapeArg {
my $arg = shift;
# Sequence of backslashes followed by a double quote:
# double up all the backslashes and escape the double quote
$arg =~ s/(\\*)"/$1$1\\"/g;
# Sequence of backslashes followed by the end of the arg,
# which will become a double quote later:
# double up all the backslashes
$arg =~ s/(\\*)$/$1$1/;
# All other backslashes do not need modifying
# Double-quote the whole thing
$arg = "\"".$arg."\"";
# Escape shell metacharacters
$arg =~ s/([()%!^"<>&|;, ])/\^$1/g;
return $arg;
}
To escape the actual command line command, for example when invoking a command with a ridiculous name such as ()!&%PATH%^;, .exe (which is perfectly legal), use the following:
sub escapeCmd {
my $arg = shift;
# Escape shell metacharacters
$arg =~ s/([()%!^"<>&|;, ])/\^$1/g;
return $arg;
}
Note that using escapeArg() for the command will not work.
Sources:
http://blogs.msdn.com/b/twistylittlepassagesallalike/archive/2011/04/23/everyone-quotes-arguments-the-wrong-way.aspx
http://support.microsoft.com/kb/103368
I want to pipe the output of a "template" file into MySQL, the file having variables like ${dbName} interspersed. What is the command line utility to replace these instances and dump the output to standard output?
The input file is considered to be safe, but faulty substitution definitions could exist. Performing the replacement should avoid performing unintended code execution.
Update
Here is a solution from yottatsa on a similar question that only does replacement for variables like $VAR or ${VAR}, and is a brief one-liner
i=32 word=foo envsubst < template.txt
Of course if i and word are in your environment, then it is just
envsubst < template.txt
On my Mac it looks like it was installed as part of gettext and from MacGPG2
Old Answer
Here is an improvement to the solution from mogsie on a similar question, my solution does not require you to escale double quotes, mogsie's does, but his is a one liner!
eval "cat <<EOF
$(<template.txt)
EOF
" 2> /dev/null
The power on these two solutions is that you only get a few types of shell expansions that don't occur normally $((...)), `...`, and $(...), though backslash is an escape character here, but you don't have to worry that the parsing has a bug, and it does multiple lines just fine.
Sed!
Given template.txt:
The number is ${i}
The word is ${word}
we just have to say:
sed -e "s/\${i}/1/" -e "s/\${word}/dog/" template.txt
Thanks to Jonathan Leffler for the tip to pass multiple -e arguments to the same sed invocation.
Use /bin/sh. Create a small shell script that sets the variables, and then parse the template using the shell itself. Like so (edit to handle newlines correctly):
File template.txt:
the number is ${i}
the word is ${word}
File script.sh:
#!/bin/sh
#Set variables
i=1
word="dog"
#Read in template one line at the time, and replace variables (more
#natural (and efficient) way, thanks to Jonathan Leffler).
while read line
do
eval echo "$line"
done < "./template.txt"
Output:
#sh script.sh
the number is 1
the word is dog
I was thinking about this again, given the recent interest, and I think that the tool that I was originally thinking of was m4, the macro processor for autotools. So instead of the variable I originally specified, you'd use:
$echo 'I am a DBNAME' | m4 -DDBNAME="database name"
Create rendertemplate.sh:
#!/usr/bin/env bash
eval "echo \"$(cat $1)\""
And template.tmpl:
Hello, ${WORLD}
Goodbye, ${CHEESE}
Render the template:
$ export WORLD=Foo
$ CHEESE=Bar ./rendertemplate.sh template.tmpl
Hello, Foo
Goodbye, Bar
template.txt
Variable 1 value: ${var1}
Variable 2 value: ${var2}
data.sh
#!/usr/bin/env bash
declare var1="value 1"
declare var2="value 2"
parser.sh
#!/usr/bin/env bash
# args
declare file_data=$1
declare file_input=$2
declare file_output=$3
source $file_data
eval "echo \"$(< $file_input)\"" > $file_output
./parser.sh data.sh template.txt parsed_file.txt
parsed_file.txt
Variable 1 value: value 1
Variable 2 value: value 2
Here's a robust Bash function that - despite using eval - should be safe to use.
All ${varName} variable references in the input text are expanded based on the calling shell's variables.
Nothing else is expanded: neither variable references whose names are not enclosed in {...} (such as $varName), nor command substitutions ($(...) and legacy syntax `...`), nor arithmetic substitutions ($((...)) and legacy syntax $[...]).
To treat a $ as a literal, \-escape it; e.g.:\${HOME}
Note that input is only accepted via stdin.
Example:
$ expandVarsStrict <<<'$HOME is "${HOME}"; `date` and \$(ls)' # only ${HOME} is expanded
$HOME is "/Users/jdoe"; `date` and $(ls)
Function source code:
expandVarsStrict(){
local line lineEscaped
while IFS= read -r line || [[ -n $line ]]; do # the `||` clause ensures that the last line is read even if it doesn't end with \n
# Escape ALL chars. that could trigger an expansion..
IFS= read -r -d '' lineEscaped < <(printf %s "$line" | tr '`([$' '\1\2\3\4')
# ... then selectively reenable ${ references
lineEscaped=${lineEscaped//$'\4'{/\${}
# Finally, escape embedded double quotes to preserve them.
lineEscaped=${lineEscaped//\"/\\\"}
eval "printf '%s\n' \"$lineEscaped\"" | tr '\1\2\3\4' '`([$'
done
}
The function assumes that no 0x1, 0x2, 0x3, and 0x4 control characters are present in the input, because those chars. are used internally - since the function processes text, that should be a safe assumption.
here's my solution with perl based on former answer, replaces environment variables:
perl -p -e 's/\$\{(\w+)\}/(exists $ENV{$1}?$ENV{$1}:"missing variable $1")/eg' < infile > outfile
I would suggest using something like Sigil:
https://github.com/gliderlabs/sigil
It is compiled to a single binary, so it's extremely easy to install on systems.
Then you can do a simple one-liner like the following:
cat my-file.conf.template | sigil -p $(env) > my-file.conf
This is much safer than eval and easier then using regex or sed
Here is a way to get the shell to do the substitution for you, as if the contents of the file were instead typed between double quotes.
Using the example of template.txt with contents:
The number is ${i}
The word is ${word}
The following line will cause the shell to interpolate the contents of template.txt and write the result to standard out.
i='1' word='dog' sh -c 'echo "'"$(cat template.txt)"'"'
Explanation:
i and word are passed as environment variables scopped to the execution of sh.
sh executes the contents of the string it is passed.
Strings written next to one another become one string, that string is:
'echo "' + "$(cat template.txt)" + '"'
Since the substitution is between ", "$(cat template.txt)" becomes the output of cat template.txt.
So the command executed by sh -c becomes:
echo "The number is ${i}\nThe word is ${word}",
where i and word are the specified environment variables.
If you are open to using Perl, that would be my suggestion. Although there are probably some sed and/or AWK experts that probably know how to do this much easier. If you have a more complex mapping with more than just dbName for your replacements you could extend this pretty easily, but you might just as well put it into a standard Perl script at that point.
perl -p -e 's/\$\{dbName\}/testdb/s' yourfile | mysql
A short Perl script to do something slightly more complicated (handle multiple keys):
#!/usr/bin/env perl
my %replace = ( 'dbName' => 'testdb', 'somethingElse' => 'fooBar' );
undef $/;
my $buf = <STDIN>;
$buf =~ s/\$\{$_\}/$replace{$_}/g for keys %replace;
print $buf;
If you name the above script as replace-script, it could then be used as follows:
replace-script < yourfile | mysql
file.tpl:
The following bash function should only replace ${var1} syntax and ignore
other shell special chars such as `backticks` or $var2 or "double quotes".
If I have missed anything - let me know.
script.sh:
template(){
# usage: template file.tpl
while read -r line ; do
line=${line//\"/\\\"}
line=${line//\`/\\\`}
line=${line//\$/\\\$}
line=${line//\\\${/\${}
eval "echo \"$line\"";
done < ${1}
}
var1="*replaced*"
var2="*not replaced*"
template file.tpl > result.txt
I found this thread while wondering the same thing. It inspired me to this (careful with the backticks)
$ echo $MYTEST
pass!
$ cat FILE
hello $MYTEST world
$ eval echo `cat FILE`
hello pass! world
Lots of choices here, but figured I'd toss mine on the heap. It is perl based, only targets variables of the form ${...}, takes the file to process as an argument and outputs the converted file on stdout:
use Env;
Env::import();
while(<>) { $_ =~ s/(\${\w+})/$1/eeg; $text .= $_; }
print "$text";
Of course I'm not really a perl person, so there could easily be a fatal flaw (works for me though).
It can be done in bash itself if you have control of the configuration file format. You just need to source (".") the configuration file rather than subshell it. That ensures the variables are created in the context of the current shell (and continue to exist) rather than the subshell (where the variable disappear when the subshell exits).
$ cat config.data
export parm_jdbc=jdbc:db2://box7.co.uk:5000/INSTA
export parm_user=pax
export parm_pwd=never_you_mind
$ cat go.bash
. config.data
echo "JDBC string is " $parm_jdbc
echo "Username is " $parm_user
echo "Password is " $parm_pwd
$ bash go.bash
JDBC string is jdbc:db2://box7.co.uk:5000/INSTA
Username is pax
Password is never_you_mind
If your config file cannot be a shell script, you can just 'compile' it before executing thus (the compilation depends on your input format).
$ cat config.data
parm_jdbc=jdbc:db2://box7.co.uk:5000/INSTA # JDBC URL
parm_user=pax # user name
parm_pwd=never_you_mind # password
$ cat go.bash
cat config.data
| sed 's/#.*$//'
| sed 's/[ \t]*$//'
| sed 's/^[ \t]*//'
| grep -v '^$'
| sed 's/^/export '
>config.data-compiled
. config.data-compiled
echo "JDBC string is " $parm_jdbc
echo "Username is " $parm_user
echo "Password is " $parm_pwd
$ bash go.bash
JDBC string is jdbc:db2://box7.co.uk:5000/INSTA
Username is pax
Password is never_you_mind
In your specific case, you could use something like:
$ cat config.data
export p_p1=val1
export p_p2=val2
$ cat go.bash
. ./config.data
echo "select * from dbtable where p1 = '$p_p1' and p2 like '$p_p2%' order by p1"
$ bash go.bash
select * from dbtable where p1 = 'val1' and p2 like 'val2%' order by p1
Then pipe the output of go.bash into MySQL and voila, hopefully you won't destroy your database :-).
In place perl editing of potentially multiple files, with backups.
perl -e 's/\$\{([^}]+)\}/defined $ENV{$1} ? $ENV{$1} : ""/eg' \
-i.orig \
-p config/test/*
I created a shell templating script named shtpl. My shtpl uses a jinja-like syntax which, now that I use ansible a lot, I'm pretty familiar with:
$ cat /tmp/test
{{ aux=4 }}
{{ myarray=( a b c d ) }}
{{ A_RANDOM=$RANDOM }}
$A_RANDOM
{% if $(( $A_RANDOM%2 )) == 0 %}
$A_RANDOM is even
{% else %}
$A_RANDOM is odd
{% endif %}
{% if $(( $A_RANDOM%2 )) == 0 %}
{% for n in 1 2 3 $aux %}
\$myarray[$((n-1))]: ${myarray[$((n-1))]}
/etc/passwd field #$n: $(grep $USER /etc/passwd | cut -d: -f$n)
{% endfor %}
{% else %}
{% for n in {1..4} %}
\$myarray[$((n-1))]: ${myarray[$((n-1))]}
/etc/group field #$n: $(grep ^$USER /etc/group | cut -d: -f$n)
{% endfor %}
{% endif %}
$ ./shtpl < /tmp/test
6535
6535 is odd
$myarray[0]: a
/etc/group field #1: myusername
$myarray[1]: b
/etc/group field #2: x
$myarray[2]: c
/etc/group field #3: 1001
$myarray[3]: d
/etc/group field #4:
More info on my github
To me this is the easiest and most powerful solution, you can even include other templates using the same command eval echo "$(<template.txt):
Example with nested template
create the template files, the variables are in regular bash syntax ${VARIABLE_NAME} or $VARIABLE_NAME
you have to escape special characters with \ in your templates otherwhise they will be interpreted by eval.
template.txt
Hello ${name}!
eval echo $(<nested-template.txt)
nested-template.txt
Nice to have you here ${name} :\)
create source file
template.source
declare name=royman
parse the template
source template.source && eval echo "$(<template.txt)"
the output
Hello royman!
Nice to have you here royman :)
envsubst
please don't use anything else (ie. don't eval)