UNIX Code Patterns (UNIX at Davar Web Site)

UNIX Code Patterns

This is a collection of code patterns for some of the common UNIX programming tasks which tend to repeat from time to time. When not singled out and classified these patterns get easily lost in the bulk of an application-specific code, and constant rewriting (and debugging) of them from scratch is a senseless waste of time.

Normally there are several ways to code the same logic, and some ways are better than the other in terms or size, effectiveness, readability and ease of modification. These criteria are rather fuzzy (except for the "size"), and are affected by personal preferences. Yet, there seems to exist a certain common sense consensus of what is "good" – like mnemonic names and labels, use of indentation, commenting, etc.

My brother Victor and I have been collecting such "good" code patterns for a long time, and this is an attempt to select the most usable of them from our scattered notes, e-mails, and scripts into one document hyperlinked for an ease of use, and accessible from anywhere and by anybody who might have interest in it. However, this selection is not compiled for the Web only – rather it's our working reference that we try to maintain as accurate and current as possible. As such it inevitably will always lack an overall integrity and completeness, yet it is still a rather useful tool that often saves time.

Most of the tasks originated from a real-life experience of a UNIX programmer. Most of the solutions were coded and debugged in the process of practical programming of various applications. Every pattern was checked to the best of my competence, and as a rule was tested by a substantial time of repeated usage. This is not to suggest that it is in any way guaranteed to be error-free – you will be using any code you pick from this selection entirely at your own risk, and will be completely responsible yourself for any problems that might arise from this usage. So when trying a code, please exercise a common sense precautions, and test it most thoroughly yourself before applying it to anything serious.

This legal mantra been chanted, I want to mention that all error reports and any comments about this code pattern selection are most welcome, and I'll try to do my best to fix any known problem as quick as I'll be able to do this.

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Korn Shell Script
MQSC (Message Queue Series Commands)

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Korn Shell Script
- Some useful predicates.
- Script execution authority checking.
- Application package information display for Solaris.
MQSC (Message Queue Series Commands)
- Some useful MQSC commands.
- WHERE filter condition.

Patterns Go to: Text top | Languages | Tasks | Index | Text bottom

Korn Shell Script

Some useful predicates.

Predicate is a logical function that returns a value of "true" or "false" (zero or non-zero return code in Korn shell). Below there are several representative examples of some often used predicates presented as "if" conditions. Some predicates have more than one possible presentation (and more than shown below), so it's a matter of taste (or circumstance) which one to choose.

[[ -z $1 ]] – Parameter 1 is empty [[ $1. = . ]] – Parameter 1 is empty [[ "$1" = "" ]] – Parameter 1 is empty (use when $1 could contain special symbols) [[ -n $1 ]] – Parameter 1 is non-empty [[ $1. != . ]] – Parameter 1 is non-empty [[ "$1" != "" ]] – Parameter 1 is non-empty (use when $1 could contain special symbols) [[ $1. = [Aa]. ]] – Parameter 1 is equal to A or a (case insensitive) [[ $1. = ^[Aa]*$. ]] – Parameter 1 starts with A or a (case insensitive) [[ $1. != [Aa]. ]] – Parameter 1 is not equal to A or a (case insensitive) [[ $1. != ^[Aa]*$. ]] – Parameter 1 doesn't start with A or a (case insensitive) [[ -a ~/.profile ]] – File ~/.profile exists [[ -d ~/script ]] – Directory ~/script exists [[ ! -a ~/.profile ]] – File ~/.profile doesn't exist [[ ! -d ~/script ]] – Directory ~/script doesn't exist

Script parameter is used as a typical example; any environment variable is equally usable in it's place, e.g.:

[[ "$Var" = "" ]] – Variable Var is empty (use when $Var could contain special symbols)

Script execution authority checking.

When execution of script requires proper authorization, it makes sense to check authority right at script entry and display a clear message to the user. The sample code pattern below checks the current user id and, if it is one of the permitted (root or mqm in this example), the main part of script code gets executed. Otherwise an authorization failure message gets displayed followed by the display of current user identification. The real-life implementation of this authorization pattern can be found in the SETMQAUT script.

User=$(id | cut -f2 -d'(' | cut -f1 -d')') if [[ $User = root || $User = mqm ]] then main_script_code else echo === Sorry, script_name script requires root or mqm echo === authority for execution, but you are $User. id fi

Application package information display for Solaris.

The pkginfo command can be used to check whether an application (with patches) is installed on Solaris server and to display information about application (version, installation date and status being the most important). (See FAQ for examples of pkginfo command usage).

When it's necessary to check one and the same application for version rather often on multiple servers, it becomes practical to have a small script (serving merely as shorthand) — best as function in the .profile — that gets the application information. Such script is specific to the application and is named accordingly. Below there is an example of gmqv (get mq version) script that displays the version of MQSeries main package and its patch, installed on Solaris server (or appropriate messages in case of missing components).

# -------- Get Version of Installed MQSeries ----------------------------------- function gmqv { if [[ "$(pkginfo | grep mqm)" = "" ]] then echo MQSeries is NOT installed on host $(hostname) else pkginfo | grep mq echo pkginfo -l mqm P=$(pkginfo | grep mqm- | awk '{print $2}') if [[ "$P" = "" ]] then echo MQSeries patch is NOT installed on host $(hostname) else pkginfo -l $P fi unset P fi; }

Below there is an example of gmqv script output showing installation information for MQSeries main package and its patch.

# gmqv application mqm MQSeries for Sun Solaris 2 application mqm-upd02 MQSeries for Sun Solaris 2 - U474789 PKGINST: mqm NAME: MQSeries for Sun Solaris 2 CATEGORY: application ARCH: sparc VERSION: 5.2.0 VENDOR: IBM PSTAMP: p000-L001106 (packaged: November 07, 2000 - 05:51:46 AM) INSTDATE: Jan 29 2001 14:53 STATUS: completely installed FILES: 2248 installed pathnames 142 executables 47 setuid/setgid executables 58599 blocks used (approx) PKGINST: mqm-upd02 NAME: MQSeries for Sun Solaris 2 - U474789 CATEGORY: application ARCH: sparc VERSION: 5.2.0 VENDOR: IBM PSTAMP: cubam15162854 INSTDATE: Jan 29 2001 15:00 STATUS: completely installed FILES: 71 installed pathnames 57 executables 28 setuid/setgid executables 22369 blocks used (approx)

MQSC (Message Queue Series Commands)

Some useful MQSC commands.

MQSeries Command utility provides a command interface to the Queue Manager (specified as a parameter for runmqsc command, or MQSeries default Queue Manager, if no parameter is specified; any further reference to "all" objects implies this Queue Manager). MQSC provides a basic functionality of creation, modification, deletion and control of MQSeries objects.

Some of MQSC most useful (and generally harmless) commands (mainly displays) are listed below. Add "descr" to any list command to get object description attribute. Add "all" to any list command to get all object attributes for every listed object. Start every interactive MQSC session with the Queue Manager display to make sure that you are working with the right one (there is no prompt). All listed objects get sorted alphabetically by name.

dis qmgr crdate – Display current Queue Manager name and creation date dis chl(*) – List all channels with their types dis chl(*) type(SDR) – List all sender channels dis chl(*) type(SVR) – List all server channels dis chl(*) type(RCVR) – List all receiver channels dis chl(*) type(SVRCONN) – List all server-connection channels dis chl(*) type(SDR) conname – List all sender channel connection names dis chl(*) type(SDR) xmitq – List all sender channel transmission queues dis chl(*) type(SVR) xmitq – List all server channel transmission queues ping chl(channel) – Ping specified non-running sender or qualified server channel dis chl(channel) – Display all attributes of the specified channel dis chs(*) – Display current status of every channel that has status data dis chs(*) saved – Display saved status of every channel that had status data dis chs(*) all – Display all current status data of every channel that has it dis chs(*) saved all – Display all saved status data of every channel that had it dis q (*) – List all queues dis ql(*) – List all local queues dis qr(*) – List all remote queues dis qa(*) – List all alias queues dis qm(*) – List all model queues dis ql(*) defpsist – Display default message persistence of every local queue dis ql(*) curdepth – Display current depth of every local queue (number of messages) dis q(queue) – Display all attributes of the specified queue clear ql(queue) – Delete all messages from specified local queue (clear queue) dis pro(*) – List all processes dis pro(process) – Display all attributes of the specified process dis chl(SYSTEM.DEF*) all – Display all default attributes for every type of channel dis q(SYSTEM.DEF*) all – Display all default attributes for every type of queue end – End MQSC session

WHERE filter condition.

With MQSeries version 6.0 that was released in 2005 the most basic where filter condition was added to MQSC display command options. Though not even coming close to a real query, it permitted a significant enhancement in flexibility of MQSC display commands. Several representative examples of where filter condition usage are shown below.

Notes:

The actual value of a parameter used in where condition gets always displayed, it doesn't need to be requested explicitly.
Add all after any command to get a detailed output. This could be too much in certain cases, so generally it's better to get a short view first, and then, where necessary, repeat command with added all for a detailed output.

dis q (*) where(defpsist EQ NO) – List all queues non-persistent by default dis ql(*) where(defpsist EQ NO) – List all local queues non-persistent by default dis qr(*) where(defpsist EQ NO) – List all remote queues non-persistent by default dis qa(*) where(defpsist EQ NO) – List all alias queues non-persistent by default dis qm(*) where(defpsist EQ NO) – List all model queues non-persistent by default dis ql(*) where(curdepth GT 99) – Display current depth of all local queues with more than 99 messages dis ql(*) curdepth where(usage EQ XMITQ) – Display current depth of all transmission queues dis chs(*) where(status NE RUNNING) – Display all channels with current status other than RUNNING dis chs(*) where(status NE STOPPED) – Display all channels with current status other than STOPPED dis chs(*) where(status EQ STOPPED) – Display all channels that are currenty STOPPED dis chs(*) where(status EQ RETRYING) – Display all channels that are currenty RETRYING dis chs(*) where(chltype EQ SDR) – Display current status of all sender channels dis chs(*) where(chltype EQ RCVR) – Display current status of all receiver channels dis chs(*) where(chltype NE SVRCONN) – Display current status of all channels except SVRCONNs dis chl(*) where(xmitq EQ xmitq) – Display names of all channels having specified xmitq dis chs(*) where(xmitq EQ xmitq) – Display status of all channels having specified xmitq

Index Go to: Text top | Languages | Tasks | Patterns | Text bottom

A
- Script execution authority checking (Korn Shell Script)

C
- Some useful MQSC commands (MQSC)

K
- Korn Shell Script

M
- MQSC (Message Queue Series Commands)

P
- Applicadion package information display for Solaris (Korn Shell Script)
- Some useful predicates (Korn Shell Script)

W
- WHERE filter condition (MQSC)